/[pcre]/code/trunk/doc/pcre.txt

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-revision 83 by nigel,
Sat Feb 24 21:41:06 2007 UTC
+revision 185 by ph10,
Tue Jun 19 13:39:46 2007 UTC
 Line 18 
 INTRODUCTION
         The  PCRE  library is a set of functions that implement regular expres-
         sion pattern matching using the same syntax and semantics as Perl, with
-        just  a  few  differences.  The current implementation of PCRE (release
+        just  a  few differences. (Certain features that appeared in Python and
-.x) corresponds approximately with Perl  5.8,  including  support  for
+        PCRE before they appeared in Perl are also available using  the  Python
-        UTF-8 encoded strings and Unicode general category properties. However,
+        syntax.)
-        this support has to be explicitly enabled; it is not the default.
+        The  current  implementation of PCRE (release 7.x) corresponds approxi-
-        In addition to the Perl-compatible matching function,  PCRE  also  con-
+        mately with Perl 5.10, including support for UTF-8 encoded strings  and
-        tains  an  alternative matching function that matches the same compiled
+        Unicode general category properties. However, UTF-8 and Unicode support
-        patterns in a different way. In certain circumstances, the  alternative
+        has to be explicitly enabled; it is not the default. The Unicode tables
-        function  has  some  advantages.  For  a discussion of the two matching
+        correspond to Unicode release 5.0.0.
-        algorithms, see the pcrematching page.
+        In  addition to the Perl-compatible matching function, PCRE contains an
-        PCRE is written in C and released as a C library. A  number  of  people
+        alternative matching function that matches the same  compiled  patterns
-        have  written  wrappers and interfaces of various kinds. In particular,
+        in  a different way. In certain circumstances, the alternative function
-        Google Inc.  have provided a comprehensive C++  wrapper.  This  is  now
+        has some advantages. For a discussion of the two  matching  algorithms,
+        see the pcrematching page.
+        PCRE  is  written  in C and released as a C library. A number of people
+        have written wrappers and interfaces of various kinds.  In  particular,
+        Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
         included as part of the PCRE distribution. The pcrecpp page has details
-        of this interface. Other people's contributions can  be  found  in  the
+        of  this  interface.  Other  people's contributions can be found in the
         Contrib directory at the primary FTP site, which is:
         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
-        Details  of  exactly which Perl regular expression features are and are
+        Details of exactly which Perl regular expression features are  and  are
         not supported by PCRE are given in separate documents. See the pcrepat-
         tern and pcrecompat pages.
-        Some  features  of  PCRE can be included, excluded, or changed when the
+        Some features of PCRE can be included, excluded, or  changed  when  the
-        library is built. The pcre_config() function makes it  possible  for  a
+        library  is  built.  The pcre_config() function makes it possible for a
-        client  to  discover  which  features are available. The features them-
+        client to discover which features are  available.  The  features  them-
-        selves are described in the pcrebuild page. Documentation about  build-
+        selves  are described in the pcrebuild page. Documentation about build-
-        ing  PCRE for various operating systems can be found in the README file
+        ing PCRE for various operating systems can be found in the README  file
         in the source distribution.
-        The library contains a number of undocumented  internal  functions  and
+        The  library  contains  a number of undocumented internal functions and
-        data  tables  that  are  used by more than one of the exported external
+        data tables that are used by more than one  of  the  exported  external
-        functions, but which are not intended  for  use  by  external  callers.
+        functions,  but  which  are  not  intended for use by external callers.
-        Their  names  all begin with "_pcre_", which hopefully will not provoke
+        Their names all begin with "_pcre_", which hopefully will  not  provoke
         any name clashes. In some environments, it is possible to control which
-        external  symbols  are  exported when a shared library is built, and in
+        external symbols are exported when a shared library is  built,  and  in
         these cases the undocumented symbols are not exported.
  USER DOCUMENTATION
-        The user documentation for PCRE comprises a number  of  different  sec-
+        The  user  documentation  for PCRE comprises a number of different sec-
-        tions.  In the "man" format, each of these is a separate "man page". In
+        tions. In the "man" format, each of these is a separate "man page".  In
-        the HTML format, each is a separate page, linked from the  index  page.
+        the  HTML  format, each is a separate page, linked from the index page.
-        In  the  plain text format, all the sections are concatenated, for ease
+        In the plain text format, all the sections are concatenated,  for  ease
         of searching. The sections are as follows:
           pcre              this document
+          pcre-config       show PCRE installation configuration information
           pcreapi           details of PCRE's native C API
           pcrebuild         options for building PCRE
           pcrecallout       details of the callout feature
-Line 81 
 USER DOCUMENTATION
+Line 87 
 USER DOCUMENTATION
           pcreposix         the POSIX-compatible C API
           pcreprecompile    details of saving and re-using precompiled patterns
           pcresample        discussion of the sample program
+          pcrestack         discussion of stack usage
           pcretest          description of the pcretest testing command
-        In  addition,  in the "man" and HTML formats, there is a short page for
+        In addition, in the "man" and HTML formats, there is a short  page  for
         each C library function, listing its arguments and results.
  LIMITATIONS
-        There are some size limitations in PCRE but it is hoped that they  will
+        There  are some size limitations in PCRE but it is hoped that they will
         never in practice be relevant.
-        The  maximum  length of a compiled pattern is 65539 (sic) bytes if PCRE
+        The maximum length of a compiled pattern is 65539 (sic) bytes  if  PCRE
         is compiled with the default internal linkage size of 2. If you want to
-        process  regular  expressions  that are truly enormous, you can compile
+        process regular expressions that are truly enormous,  you  can  compile
-        PCRE with an internal linkage size of 3 or 4 (see the  README  file  in
+        PCRE  with  an  internal linkage size of 3 or 4 (see the README file in
-        the  source  distribution and the pcrebuild documentation for details).
+        the source distribution and the pcrebuild documentation  for  details).
-        In these cases the limit is substantially larger.  However,  the  speed
+        In  these  cases the limit is substantially larger.  However, the speed
-        of execution will be slower.
+        of execution is slower.
-        All values in repeating quantifiers must be less than 65536.  The maxi-
+        All values in repeating quantifiers must be less than 65536. The  maxi-
-        mum number of capturing subpatterns is 65535.
+        mum  compiled  length  of  subpattern  with an explicit repeat count is
+bytes. The maximum number of capturing subpatterns is 65535.
-        There is no limit to the number of non-capturing subpatterns,  but  the
-        maximum  depth  of  nesting  of  all kinds of parenthesized subpattern,
-        including capturing subpatterns, assertions, and other types of subpat-
-        tern, is 200.
-        The  maximum  length of a subject string is the largest positive number
+        There is no limit to the number of parenthesized subpatterns, but there
-        that an integer variable can hold. However, when using the  traditional
+        can be no more than 65535 capturing subpatterns.
+        The maximum length of name for a named subpattern is 32 characters, and
+        the maximum number of named subpatterns is 10000.
+        The maximum length of a subject string is the largest  positive  number
+        that  an integer variable can hold. However, when using the traditional
         matching function, PCRE uses recursion to handle subpatterns and indef-
-        inite repetition.  This means that the available stack space may  limit
+        inite  repetition.  This means that the available stack space may limit
         the size of a subject string that can be processed by certain patterns.
+        For a discussion of stack issues, see the pcrestack documentation.
  UTF-8 AND UNICODE PROPERTY SUPPORT
-        From release 3.3, PCRE has  had  some  support  for  character  strings
+        From  release  3.3,  PCRE  has  had  some support for character strings
-        encoded  in the UTF-8 format. For release 4.0 this was greatly extended
+        encoded in the UTF-8 format. For release 4.0 this was greatly  extended
-        to cover most common requirements, and in release 5.0  additional  sup-
+        to  cover  most common requirements, and in release 5.0 additional sup-
         port for Unicode general category properties was added.
-        In  order  process  UTF-8 strings, you must build PCRE to include UTF-8
+        In order process UTF-8 strings, you must build PCRE  to  include  UTF-8
-        support in the code, and, in addition,  you  must  call  pcre_compile()
+        support  in  the  code,  and, in addition, you must call pcre_compile()
-        with  the PCRE_UTF8 option flag. When you do this, both the pattern and
+        with the PCRE_UTF8 option flag. When you do this, both the pattern  and
-        any subject strings that are matched against it are  treated  as  UTF-8
+        any  subject  strings  that are matched against it are treated as UTF-8
         strings instead of just strings of bytes.
-        If  you compile PCRE with UTF-8 support, but do not use it at run time,
+        If you compile PCRE with UTF-8 support, but do not use it at run  time,
-        the library will be a bit bigger, but the additional run time  overhead
+        the  library will be a bit bigger, but the additional run time overhead
-        is  limited  to testing the PCRE_UTF8 flag in several places, so should
+        is limited to testing the PCRE_UTF8 flag occasionally, so should not be
-        not be very large.
+        very big.
         If PCRE is built with Unicode character property support (which implies
-        UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-
+        UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
         ported.  The available properties that can be tested are limited to the
-        general  category  properties such as Lu for an upper case letter or Nd
+        general category properties such as Lu for an upper case letter  or  Nd
-        for a decimal number. A full list is given in the pcrepattern  documen-
+        for  a  decimal number, the Unicode script names such as Arabic or Han,
-        tation. The PCRE library is increased in size by about 90K when Unicode
+        and the derived properties Any and L&. A full  list  is  given  in  the
-        property support is included.
+        pcrepattern documentation. Only the short names for properties are sup-
+        ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
+        ter},  is  not  supported.   Furthermore,  in Perl, many properties may
+        optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
+        does not support this.
         The following comments apply when PCRE is running in UTF-8 mode:
-. When you set the PCRE_UTF8 flag, the strings passed as patterns  and
+.  When you set the PCRE_UTF8 flag, the strings passed as patterns and
-        subjects  are  checked for validity on entry to the relevant functions.
+        subjects are checked for validity on entry to the  relevant  functions.
         If an invalid UTF-8 string is passed, an error return is given. In some
-        situations,  you  may  already  know  that  your strings are valid, and
+        situations, you may already know  that  your  strings  are  valid,  and
         therefore want to skip these checks in order to improve performance. If
-        you  set  the  PCRE_NO_UTF8_CHECK  flag at compile time or at run time,
+        you set the PCRE_NO_UTF8_CHECK flag at compile time  or  at  run  time,
-        PCRE assumes that the pattern or subject  it  is  given  (respectively)
+        PCRE  assumes  that  the  pattern or subject it is given (respectively)
-        contains  only valid UTF-8 codes. In this case, it does not diagnose an
+        contains only valid UTF-8 codes. In this case, it does not diagnose  an
-        invalid UTF-8 string. If you pass an invalid UTF-8 string to PCRE  when
+        invalid  UTF-8 string. If you pass an invalid UTF-8 string to PCRE when
-        PCRE_NO_UTF8_CHECK  is set, the results are undefined. Your program may
+        PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program  may
         crash.
-. In a pattern, the escape sequence \x{...}, where the contents of the
+.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
-        braces  is  a  string  of hexadecimal digits, is interpreted as a UTF-8
+        two-byte UTF-8 character if the value is greater than 127.
-        character whose code number is the given hexadecimal number, for  exam-
-        ple:  \x{1234}.  If a non-hexadecimal digit appears between the braces,
-        the item is not recognized.  This escape sequence can be used either as
-        a literal, or within a character class.
-.  The  original hexadecimal escape sequence, \xhh, matches a two-byte
+. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8
-        UTF-8 character if the value is greater than 127.
+        characters for values greater than \177.
-. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-
+.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
         vidual bytes, for example: \x{100}{3}.
-.  The dot metacharacter matches one UTF-8 character instead of a sin-
+. The dot metacharacter matches one UTF-8 character instead of a  sin-
         gle byte.
-. The escape sequence \C can be used to match a single byte  in  UTF-8
+.  The  escape sequence \C can be used to match a single byte in UTF-8
-        mode,  but  its  use can lead to some strange effects. This facility is
+        mode, but its use can lead to some strange effects.  This  facility  is
         not available in the alternative matching function, pcre_dfa_exec().
-. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly
+.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
-        test  characters of any code value, but the characters that PCRE recog-
+        test characters of any code value, but the characters that PCRE  recog-
-        nizes as digits, spaces, or word characters  remain  the  same  set  as
+        nizes  as  digits,  spaces,  or  word characters remain the same set as
         before, all with values less than 256. This remains true even when PCRE
-        includes Unicode property support, because to do otherwise  would  slow
+        includes  Unicode  property support, because to do otherwise would slow
-        down  PCRE in many common cases. If you really want to test for a wider
+        down PCRE in many common cases. If you really want to test for a  wider
-        sense of, say, "digit", you must use Unicode  property  tests  such  as
+        sense  of,  say,  "digit",  you must use Unicode property tests such as
         \p{Nd}.
-.  Similarly,  characters that match the POSIX named character classes
+. Similarly, characters that match the POSIX named  character  classes
         are all low-valued characters.
-. Case-insensitive matching applies only to  characters  whose  values
+.  However,  the Perl 5.10 horizontal and vertical whitespace matching
-        are  less than 128, unless PCRE is built with Unicode property support.
+        escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
-        Even when Unicode property support is available, PCRE  still  uses  its
+        acters.
-        own  character  tables when checking the case of low-valued characters,
-        so as not to degrade performance.  The Unicode property information  is
+.  Case-insensitive  matching applies only to characters whose values
-        used only for characters with higher values.
+        are less than 128, unless PCRE is built with Unicode property  support.
+        Even  when  Unicode  property support is available, PCRE still uses its
+        own character tables when checking the case of  low-valued  characters,
+        so  as not to degrade performance.  The Unicode property information is
+        used only for characters with higher values. Even when Unicode property
+        support is available, PCRE supports case-insensitive matching only when
+        there is a one-to-one mapping between a letter's  cases.  There  are  a
+        small  number  of  many-to-one  mappings in Unicode; these are not sup-
+        ported by PCRE.
  AUTHOR
         Philip Hazel
-        University Computing Service,
+        University Computing Service
-        Cambridge CB2 3QG, England.
+        Cambridge CB2 3QH, England.
+        Putting an actual email address here seems to have been a spam  magnet,
+        so  I've  taken  it away. If you want to email me, use my two initials,
+        followed by the two digits 10, at the domain cam.ac.uk.
-        Putting  an actual email address here seems to have been a spam magnet,
+ REVISION
-        so I've taken it away. If you want to email me, use my initial and sur-
-        name, separated by a dot, at the domain ucs.cam.ac.uk.
- Last updated: 07 March 2005
+        Last updated: 13 June 2007
- Copyright (c) 1997-2005 University of Cambridge.
+        Copyright (c) 1997-2007 University of Cambridge.
  ------------------------------------------------------------------------------
-Line 228 
 PCRE BUILD-TIME OPTIONS
+Line 249 
 PCRE BUILD-TIME OPTIONS
           ./configure --help
-        The following sections describe certain options whose names begin  with
+        The following sections include  descriptions  of  options  whose  names
-        --enable  or  --disable. These settings specify changes to the defaults
+        begin with --enable or --disable. These settings specify changes to the
-        for the configure command. Because of the  way  that  configure  works,
+        defaults for the configure command. Because of the way  that  configure
-        --enable  and  --disable  always  come  in  pairs, so the complementary
+        works,  --enable  and --disable always come in pairs, so the complemen-
-        option always exists as well, but as it specifies the  default,  it  is
+        tary option always exists as well, but as it specifies the default,  it
-        not described.
+        is not described.
  C++ SUPPORT
-Line 272 
 UNICODE CHARACTER PROPERTY SUPPORT
+Line 293 
 UNICODE CHARACTER PROPERTY SUPPORT
         to the configure command. This implies UTF-8 support, even if you  have
         not explicitly requested it.
-        Including  Unicode  property  support  adds around 90K of tables to the
+        Including  Unicode  property  support  adds around 30K of tables to the
-        PCRE library, approximately doubling its size. Only the  general  cate-
+        PCRE library. Only the general category properties such as  Lu  and  Nd
-        gory  properties  such as Lu and Nd are supported. Details are given in
+        are supported. Details are given in the pcrepattern documentation.
-        the pcrepattern documentation.
  CODE VALUE OF NEWLINE
-        By default, PCRE treats character 10 (linefeed) as the newline  charac-
+        By  default,  PCRE interprets character 10 (linefeed, LF) as indicating
-        ter. This is the normal newline character on Unix-like systems. You can
+        the end of a line. This is the normal newline  character  on  Unix-like
-        compile PCRE to use character 13 (carriage return) instead by adding
+        systems. You can compile PCRE to use character 13 (carriage return, CR)
+        instead, by adding
           --enable-newline-is-cr
-        to the configure command. For completeness there is  also  a  --enable-
+        to the  configure  command.  There  is  also  a  --enable-newline-is-lf
-        newline-is-lf  option,  which explicitly specifies linefeed as the new-
+        option, which explicitly specifies linefeed as the newline character.
-        line character.
+        Alternatively, you can specify that line endings are to be indicated by
+        the two character sequence CRLF. If you want this, add
+          --enable-newline-is-crlf
+        to the configure command. There is a fourth option, specified by
+          --enable-newline-is-anycrlf
+        which causes PCRE to recognize any of the three sequences  CR,  LF,  or
+        CRLF as indicating a line ending. Finally, a fifth option, specified by
+          --enable-newline-is-any
+        causes PCRE to recognize any Unicode newline sequence.
+        Whatever line ending convention is selected when PCRE is built  can  be
+        overridden  when  the library functions are called. At build time it is
+        conventional to use the standard for your operating system.
  BUILDING SHARED AND STATIC LIBRARIES
-Line 319 
 POSIX MALLOC USAGE
+Line 359 
 POSIX MALLOC USAGE
         to the configure command.
- LIMITING PCRE RESOURCE USAGE
-        Internally,  PCRE has a function called match(), which it calls repeat-
-        edly  (possibly  recursively)  when  matching  a   pattern   with   the
-        pcre_exec()  function.  By controlling the maximum number of times this
-        function may be called during a single matching operation, a limit  can
-        be  placed  on  the resources used by a single call to pcre_exec(). The
-        limit can be changed at run time, as described in the pcreapi  documen-
-        tation.  The default is 10 million, but this can be changed by adding a
-        setting such as
-          --with-match-limit=500000
-        to  the  configure  command.  This  setting  has  no  effect   on   the
-        pcre_dfa_exec() matching function.
  HANDLING VERY LARGE PATTERNS
         Within  a  compiled  pattern,  offset values are used to point from one
-Line 353 
 HANDLING VERY LARGE PATTERNS
+Line 376 
 HANDLING VERY LARGE PATTERNS
         longer  offsets slows down the operation of PCRE because it has to load
         additional bytes when handling them.
-        If you build PCRE with an increased link size, test 2 (and  test  5  if
-        you  are using UTF-8) will fail. Part of the output of these tests is a
-        representation of the compiled pattern, and this changes with the  link
-        size.
  AVOIDING EXCESSIVE STACK USAGE
         When matching with the pcre_exec() function, PCRE implements backtrack-
-        ing by making recursive calls to an internal function  called  match().
+        ing  by  making recursive calls to an internal function called match().
-        In  environments  where  the size of the stack is limited, this can se-
+        In environments where the size of the stack is limited,  this  can  se-
-        verely limit PCRE's operation. (The Unix environment does  not  usually
+        verely  limit  PCRE's operation. (The Unix environment does not usually
-        suffer  from  this  problem.)  An alternative approach that uses memory
+        suffer from this problem, but it may sometimes be necessary to increase
-        from the heap to remember data, instead  of  using  recursive  function
+        the  maximum  stack size.  There is a discussion in the pcrestack docu-
-        calls,  has been implemented to work round this problem. If you want to
+        mentation.) An alternative approach to recursion that uses memory  from
-        build a version of PCRE that works this way, add
+        the  heap  to remember data, instead of using recursive function calls,
+        has been implemented to work round the problem of limited  stack  size.
+        If you want to build a version of PCRE that works this way, add
           --disable-stack-for-recursion
-        to the configure command. With this configuration, PCRE  will  use  the
+        to  the  configure  command. With this configuration, PCRE will use the
-        pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
+        pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
-        ment functions. Separate functions are provided because  the  usage  is
+        ment  functions. By default these point to malloc() and free(), but you
-        very  predictable:  the  block sizes requested are always the same, and
+        can replace the pointers so that your own functions are used.
-        the blocks are always freed in reverse order. A calling  program  might
-        be  able  to implement optimized functions that perform better than the
+        Separate functions are  provided  rather  than  using  pcre_malloc  and
-        standard malloc() and  free()  functions.  PCRE  runs  noticeably  more
+        pcre_free  because  the  usage  is  very  predictable:  the block sizes
-        slowly when built in this way. This option affects only the pcre_exec()
+        requested are always the same, and  the  blocks  are  always  freed  in
-        function; it is not relevant for the the pcre_dfa_exec() function.
+        reverse  order.  A calling program might be able to implement optimized
+        functions that perform better  than  malloc()  and  free().  PCRE  runs
+        noticeably more slowly when built in this way. This option affects only
+        the  pcre_exec()  function;  it   is   not   relevant   for   the   the
+        pcre_dfa_exec() function.
+ LIMITING PCRE RESOURCE USAGE
+        Internally,  PCRE has a function called match(), which it calls repeat-
+        edly  (sometimes  recursively)  when  matching  a  pattern   with   the
+        pcre_exec()  function.  By controlling the maximum number of times this
+        function may be called during a single matching operation, a limit  can
+        be  placed  on  the resources used by a single call to pcre_exec(). The
+        limit can be changed at run time, as described in the pcreapi  documen-
+        tation.  The default is 10 million, but this can be changed by adding a
+        setting such as
+          --with-match-limit=500000
+        to  the  configure  command.  This  setting  has  no  effect   on   the
+        pcre_dfa_exec() matching function.
+        In  some  environments  it is desirable to limit the depth of recursive
+        calls of match() more strictly than the total number of calls, in order
+        to  restrict  the maximum amount of stack (or heap, if --disable-stack-
+        for-recursion is specified) that is used. A second limit controls this;
+        it  defaults  to  the  value  that is set for --with-match-limit, which
+        imposes no additional constraints. However, you can set a  lower  limit
+        by adding, for example,
+          --with-match-limit-recursion=10000
+        to  the  configure  command.  This  value can also be overridden at run
+        time.
+ CREATING CHARACTER TABLES AT BUILD TIME
+        PCRE uses fixed tables for processing characters whose code values  are
+        less  than 256. By default, PCRE is built with a set of tables that are
+        distributed in the file pcre_chartables.c.dist. These  tables  are  for
+        ASCII codes only. If you add
+          --enable-rebuild-chartables
+        to  the  configure  command, the distributed tables are no longer used.
+        Instead, a program called dftables is compiled and  run.  This  outputs
+        the source for new set of tables, created in the default locale of your
+        C runtime system. (This method of replacing the tables does not work if
+        you  are cross compiling, because dftables is run on the local host. If
+        you need to create alternative tables when cross  compiling,  you  will
+        have to do so "by hand".)
  USING EBCDIC CODE
-        PCRE assumes by default that it will run in an  environment  where  the
+        PCRE  assumes  by  default that it will run in an environment where the
-        character  code  is  ASCII  (or Unicode, which is a superset of ASCII).
+        character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
-        PCRE can, however, be compiled to  run  in  an  EBCDIC  environment  by
+        PCRE  can,  however,  be  compiled  to  run in an EBCDIC environment by
         adding
           --enable-ebcdic
-        to the configure command.
+        to the configure command. This setting implies --enable-rebuild-charta-
+        bles.
+ SEE ALSO
+        pcreapi(3), pcre_config(3).
- Last updated: 15 August 2005
- Copyright (c) 1997-2005 University of Cambridge.
+ AUTHOR
+        Philip Hazel
+        University Computing Service
+        Cambridge CB2 3QH, England.
+ REVISION
+        Last updated: 05 June 2007
+        Copyright (c) 1997-2007 University of Cambridge.
  ------------------------------------------------------------------------------
-Line 431 
 PCRE MATCHING ALGORITHMS
+Line 519 
 PCRE MATCHING ALGORITHMS
           <something> <something else> <something further>
         there are three possible answers. The standard algorithm finds only one
-        of them, whereas the DFA algorithm finds all three.
+        of them, whereas the alternative algorithm finds all three.
  REGULAR EXPRESSIONS AS TREES
-Line 440 
 REGULAR EXPRESSIONS AS TREES
+Line 528 
 REGULAR EXPRESSIONS AS TREES
         resented  as  a  tree structure. An unlimited repetition in the pattern
         makes the tree of infinite size, but it is still a tree.  Matching  the
         pattern  to a given subject string (from a given starting point) can be
-        thought of as a search of the tree.  There are  two  standard  ways  to
+        thought of as a search of the tree.  There are two  ways  to  search  a
-        search  a  tree: depth-first and breadth-first, and these correspond to
+        tree:  depth-first  and  breadth-first, and these correspond to the two
-        the two matching algorithms provided by PCRE.
+        matching algorithms provided by PCRE.
  THE STANDARD MATCHING ALGORITHM
-        In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-
+        In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
-        sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a
+        sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
         depth-first search of the pattern tree. That is, it  proceeds  along  a
         single path through the tree, checking that the subject matches what is
         required. When there is a mismatch, the algorithm  tries  any  alterna-
-Line 472 
 THE STANDARD MATCHING ALGORITHM
+Line 560 
 THE STANDARD MATCHING ALGORITHM
         This provides support for capturing parentheses and back references.
- THE DFA MATCHING ALGORITHM
+ THE ALTERNATIVE MATCHING ALGORITHM
-        DFA stands for "deterministic finite automaton", but you do not need to
+        This algorithm conducts a breadth-first search of  the  tree.  Starting
-        understand the origins of that name. This algorithm conducts a breadth-
+        from  the  first  matching  point  in the subject, it scans the subject
-        first search of the tree. Starting from the first matching point in the
+        string from left to right, once, character by character, and as it does
-        subject,  it scans the subject string from left to right, once, charac-
+        this,  it remembers all the paths through the tree that represent valid
-        ter by character, and as it does  this,  it  remembers  all  the  paths
+        matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
-        through the tree that represent valid matches.
+        though  it is not implemented as a traditional finite state machine (it
+        keeps multiple states active simultaneously).
-        The  scan  continues until either the end of the subject is reached, or
-        there are no more unterminated paths. At this point,  terminated  paths
+        The scan continues until either the end of the subject is  reached,  or
-        represent  the different matching possibilities (if there are none, the
+        there  are  no more unterminated paths. At this point, terminated paths
-        match has failed).  Thus, if there is more  than  one  possible  match,
+        represent the different matching possibilities (if there are none,  the
+        match  has  failed).   Thus,  if there is more than one possible match,
         this algorithm finds all of them, and in particular, it finds the long-
-        est. In PCRE, there is an option to stop the algorithm after the  first
+        est.  In PCRE, there is an option to stop the algorithm after the first
         match (which is necessarily the shortest) has been found.
         Note that all the matches that are found start at the same point in the
-Line 494 
 THE DFA MATCHING ALGORITHM
+Line 583 
 THE DFA MATCHING ALGORITHM
           cat(er(pillar)?)
-        is matched against the string "the caterpillar catchment",  the  result
+        is  matched  against the string "the caterpillar catchment", the result
-        will  be the three strings "cat", "cater", and "caterpillar" that start
+        will be the three strings "cat", "cater", and "caterpillar" that  start
         at the fourth character of the subject. The algorithm does not automat-
         ically move on to find matches that start at later positions.
         There are a number of features of PCRE regular expressions that are not
-        supported by the DFA matching algorithm. They are as follows:
+        supported by the alternative matching algorithm. They are as follows:
-. Because the algorithm finds all  possible  matches,  the  greedy  or
+.  Because  the  algorithm  finds  all possible matches, the greedy or
-        ungreedy  nature  of repetition quantifiers is not relevant. Greedy and
+        ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
-        ungreedy quantifiers are treated in exactly the same way.
+        ungreedy quantifiers are treated in exactly the same way. However, pos-
+        sessive quantifiers can make a difference when what follows could  also
+        match what is quantified, for example in a pattern like this:
+          ^a++\w!
+        This  pattern matches "aaab!" but not "aaa!", which would be matched by
+        a non-possessive quantifier. Similarly, if an atomic group is  present,
+        it  is matched as if it were a standalone pattern at the current point,
+        and the longest match is then "locked in" for the rest of  the  overall
+        pattern.
 . When dealing with multiple paths through the tree simultaneously, it
-        is  not  straightforward  to  keep track of captured substrings for the
+        is not straightforward to keep track of  captured  substrings  for  the
-        different matching possibilities, and  PCRE's  implementation  of  this
+        different  matching  possibilities,  and  PCRE's implementation of this
         algorithm does not attempt to do this. This means that no captured sub-
         strings are available.
-. Because no substrings are captured, back references within the  pat-
+.  Because no substrings are captured, back references within the pat-
         tern are not supported, and cause errors if encountered.
-.  For  the same reason, conditional expressions that use a backrefer-
+. For the same reason, conditional expressions that use  a  backrefer-
-        ence as the condition are not supported.
+        ence  as  the  condition or test for a specific group recursion are not
+        supported.
-. Callouts are supported, but the value of the  capture_top  field  is
+. Because many paths through the tree may be  active,  the  \K  escape
+        sequence, which resets the start of the match when encountered (but may
+        be on some paths and not on others), is not  supported.  It  causes  an
+        error if encountered.
+.  Callouts  are  supported, but the value of the capture_top field is
         always 1, and the value of the capture_last field is always -1.
 .  The \C escape sequence, which (in the standard algorithm) matches a
-        single byte, even in UTF-8 mode, is not supported because the DFA algo-
+        single  byte, even in UTF-8 mode, is not supported because the alterna-
-        rithm moves through the subject string one character at a time, for all
+        tive algorithm moves through the subject  string  one  character  at  a
-        active paths through the tree.
+        time, for all active paths through the tree.
- ADVANTAGES OF THE DFA ALGORITHM
+ ADVANTAGES OF THE ALTERNATIVE ALGORITHM
-        Using the DFA matching algorithm provides the following advantages:
+        Using  the alternative matching algorithm provides the following advan-
+        tages:
 . All possible matches (at a single point in the subject) are automat-
         ically  found,  and  in particular, the longest match is found. To find
-Line 538 
 ADVANTAGES OF THE DFA ALGORITHM
+Line 644 
 ADVANTAGES OF THE DFA ALGORITHM
 .  There is much better support for partial matching. The restrictions
         on the content of the pattern that apply when using the standard  algo-
-        rithm  for partial matching do not apply to the DFA algorithm. For non-
+        rithm  for  partial matching do not apply to the alternative algorithm.
-        anchored patterns, the starting position of a partial match  is  avail-
+        For non-anchored patterns, the starting position of a partial match  is
-        able.
+        available.
-.  Because  the  DFA algorithm scans the subject string just once, and
+.  Because  the  alternative  algorithm  scans the subject string just
-        never needs to backtrack, it is possible  to  pass  very  long  subject
+        once, and never needs to backtrack, it is possible to  pass  very  long
-        strings  to  the matching function in several pieces, checking for par-
+        subject  strings  to  the matching function in several pieces, checking
-        tial matching each time.
+        for partial matching each time.
- DISADVANTAGES OF THE DFA ALGORITHM
+ DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
-        The DFA algorithm suffers from a number of disadvantages:
+        The alternative algorithm suffers from a number of disadvantages:
 . It is substantially slower than  the  standard  algorithm.  This  is
         partly  because  it has to search for all possible matches, but is also
-Line 558 
 DISADVANTAGES OF THE DFA ALGORITHM
+Line 664 
 DISADVANTAGES OF THE DFA ALGORITHM
 . Capturing parentheses and back references are not supported.
-. The "atomic group" feature of PCRE regular expressions is supported,
+. Although atomic groups are supported, their use does not provide the
-        but  does not provide the advantage that it does for the standard algo-
+        performance advantage that it does for the standard algorithm.
-        rithm.
+ AUTHOR
+        Philip Hazel
+        University Computing Service
+        Cambridge CB2 3QH, England.
- Last updated: 28 February 2005
+ REVISION
- Copyright (c) 1997-2005 University of Cambridge.
+        Last updated: 29 May 2007
+        Copyright (c) 1997-2007 University of Cambridge.
  ------------------------------------------------------------------------------
-Line 616 
 PCRE NATIVE API
+Line 731 
 PCRE NATIVE API
         int pcre_get_stringnumber(const pcre *code,
              const char *name);
+        int pcre_get_stringtable_entries(const pcre *code,
+             const char *name, char **first, char **last);
         int pcre_get_substring(const char *subject, int *ovector,
              int stringcount, int stringnumber,
              const char **stringptr);
-Line 654 
 PCRE NATIVE API
+Line 772 
 PCRE NATIVE API
  PCRE API OVERVIEW
         PCRE has its own native API, which is described in this document. There
-        is also a set of wrapper functions that correspond to the POSIX regular
+        are also some wrapper functions that correspond to  the  POSIX  regular
         expression  API.  These  are  described in the pcreposix documentation.
         Both of these APIs define a set of C function calls. A C++  wrapper  is
         distributed with PCRE. It is documented in the pcrecpp page.
-Line 676 
 PCRE API OVERVIEW
+Line 794 
 PCRE API OVERVIEW
         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
         ble,  is  also provided. This uses a different algorithm for the match-
-        ing. This allows it to find all possible matches (at a given  point  in
+        ing. The alternative algorithm finds all possible matches (at  a  given
-        the  subject),  not  just  one. However, this algorithm does not return
+        point  in  the subject), and scans the subject just once. However, this
-        captured substrings. A description of the two matching  algorithms  and
+        algorithm does not return captured substrings. A description of the two
-        their  advantages  and disadvantages is given in the pcrematching docu-
+        matching  algorithms and their advantages and disadvantages is given in
-        mentation.
+        the pcrematching documentation.
         In addition to the main compiling and  matching  functions,  there  are
         convenience functions for extracting captured substrings from a subject
-Line 692 
 PCRE API OVERVIEW
+Line 810 
 PCRE API OVERVIEW
           pcre_get_named_substring()
           pcre_get_substring_list()
           pcre_get_stringnumber()
+          pcre_get_stringtable_entries()
         pcre_free_substring() and pcre_free_substring_list() are also provided,
         to free the memory used for extracted strings.
-Line 723 
 PCRE API OVERVIEW
+Line 842 
 PCRE API OVERVIEW
         indirections  to  memory  management functions. These special functions
         are used only when PCRE is compiled to use  the  heap  for  remembering
         data, instead of recursive function calls, when running the pcre_exec()
-        function. This is a non-standard way of building PCRE, for use in envi-
+        function. See the pcrebuild documentation for  details  of  how  to  do
-        ronments that have limited stacks. Because of the greater use of memory
+        this.  It  is  a non-standard way of building PCRE, for use in environ-
-        management, it runs more slowly.  Separate functions  are  provided  so
+        ments that have limited stacks. Because of the greater  use  of  memory
-        that  special-purpose  external  code  can  be used for this case. When
+        management,  it  runs  more  slowly. Separate functions are provided so
-        used, these functions are always called in a  stack-like  manner  (last
+        that special-purpose external code can be  used  for  this  case.  When
-        obtained,  first freed), and always for memory blocks of the same size.
+        used,  these  functions  are always called in a stack-like manner (last
+        obtained, first freed), and always for memory blocks of the same  size.
+        There  is  a discussion about PCRE's stack usage in the pcrestack docu-
+        mentation.
         The global variable pcre_callout initially contains NULL. It can be set
         by  the  caller  to  a "callout" function, which PCRE will then call at
-Line 736 
 PCRE API OVERVIEW
+Line 858 
 PCRE API OVERVIEW
         pcrecallout documentation.
+ NEWLINES
+        PCRE  supports five different conventions for indicating line breaks in
+        strings: a single CR (carriage return) character, a  single  LF  (line-
+        feed) character, the two-character sequence CRLF, any of the three pre-
+        ceding, or any Unicode newline sequence. The Unicode newline  sequences
+        are  the  three just mentioned, plus the single characters VT (vertical
+        tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
+        separator, U+2028), and PS (paragraph separator, U+2029).
+        Each  of  the first three conventions is used by at least one operating
+        system as its standard newline sequence. When PCRE is built, a  default
+        can  be  specified.  The default default is LF, which is the Unix stan-
+        dard. When PCRE is run, the default can be overridden,  either  when  a
+        pattern is compiled, or when it is matched.
+        In the PCRE documentation the word "newline" is used to mean "the char-
+        acter or pair of characters that indicate a line break". The choice  of
+        newline  convention  affects  the  handling of the dot, circumflex, and
+        dollar metacharacters, the handling of #-comments in /x mode, and, when
+        CRLF  is a recognized line ending sequence, the match position advance-
+        ment for a non-anchored pattern. The choice of newline convention  does
+        not affect the interpretation of the \n or \r escape sequences.
  MULTITHREADING
         The  PCRE  functions  can be used in multi-threading applications, with
-Line 753 
 SAVING PRECOMPILED PATTERNS FOR LATER US
+Line 900 
 SAVING PRECOMPILED PATTERNS FOR LATER US
         The compiled form of a regular expression can be saved and re-used at a
         later time, possibly by a different program, and even on a  host  other
         than  the  one  on  which  it  was  compiled.  Details are given in the
-        pcreprecompile documentation.
+        pcreprecompile documentation. However, compiling a  regular  expression
+        with  one version of PCRE for use with a different version is not guar-
+        anteed to work and may cause crashes.
  CHECKING BUILD-TIME OPTIONS
-Line 782 
 CHECKING BUILD-TIME OPTIONS
+Line 931 
 CHECKING BUILD-TIME OPTIONS
           PCRE_CONFIG_NEWLINE
-        The output is an integer that is set to the value of the code  that  is
+        The output is an integer whose value specifies  the  default  character
-        used  for the newline character. It is either linefeed (10) or carriage
+        sequence  that is recognized as meaning "newline". The four values that
-        return (13), and should normally be the  standard  character  for  your
+        are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
-        operating system.
+        and  -1  for  ANY. The default should normally be the standard sequence
+        for your operating system.
           PCRE_CONFIG_LINK_SIZE
-        The  output  is  an  integer that contains the number of bytes used for
+        The output is an integer that contains the number  of  bytes  used  for
         internal linkage in compiled regular expressions. The value is 2, 3, or
-.  Larger  values  allow larger regular expressions to be compiled, at
+. Larger values allow larger regular expressions to  be  compiled,  at
-        the expense of slower matching. The default value of  2  is  sufficient
+        the  expense  of  slower matching. The default value of 2 is sufficient
-        for  all  but  the  most massive patterns, since it allows the compiled
+        for all but the most massive patterns, since  it  allows  the  compiled
         pattern to be up to 64K in size.
           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
-        The output is an integer that contains the threshold  above  which  the
+        The  output  is  an integer that contains the threshold above which the
-        POSIX  interface  uses malloc() for output vectors. Further details are
+        POSIX interface uses malloc() for output vectors. Further  details  are
         given in the pcreposix documentation.
           PCRE_CONFIG_MATCH_LIMIT
         The output is an integer that gives the default limit for the number of
-        internal  matching  function  calls in a pcre_exec() execution. Further
+        internal matching function calls in a  pcre_exec()  execution.  Further
         details are given with pcre_exec() below.
+          PCRE_CONFIG_MATCH_LIMIT_RECURSION
+        The  output is an integer that gives the default limit for the depth of
+        recursion when calling the internal matching function in a  pcre_exec()
+        execution. Further details are given with pcre_exec() below.
           PCRE_CONFIG_STACKRECURSE
-        The output is an integer that is set to one if internal recursion  when
+        The  output is an integer that is set to one if internal recursion when
         running pcre_exec() is implemented by recursive function calls that use
-        the stack to remember their state. This is the usual way that  PCRE  is
+        the  stack  to remember their state. This is the usual way that PCRE is
         compiled. The output is zero if PCRE was compiled to use blocks of data
-        on the  heap  instead  of  recursive  function  calls.  In  this  case,
+        on  the  heap  instead  of  recursive  function  calls.  In  this case,
-        pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory
+        pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
         blocks on the heap, thus avoiding the use of the stack.
-Line 832 
 COMPILING A PATTERN
+Line 988 
 COMPILING A PATTERN
         Either of the functions pcre_compile() or pcre_compile2() can be called
         to compile a pattern into an internal form. The only difference between
-        the two interfaces is that pcre_compile2() has an additional  argument,
+        the  two interfaces is that pcre_compile2() has an additional argument,
         errorcodeptr, via which a numerical error code can be returned.
         The pattern is a C string terminated by a binary zero, and is passed in
-        the pattern argument. A pointer to a single block  of  memory  that  is
+        the  pattern  argument.  A  pointer to a single block of memory that is
-        obtained  via  pcre_malloc is returned. This contains the compiled code
+        obtained via pcre_malloc is returned. This contains the  compiled  code
         and related data. The pcre type is defined for the returned block; this
         is a typedef for a structure whose contents are not externally defined.
-        It is up to the caller  to  free  the  memory  when  it  is  no  longer
+        It is up to the caller to free the memory (via pcre_free) when it is no
-        required.
+        longer required.
-        Although  the compiled code of a PCRE regex is relocatable, that is, it
+        Although the compiled code of a PCRE regex is relocatable, that is,  it
         does not depend on memory location, the complete pcre data block is not
-        fully  relocatable, because it may contain a copy of the tableptr argu-
+        fully relocatable, because it may contain a copy of the tableptr  argu-
         ment, which is an address (see below).
-        The options argument contains independent bits that affect the compila-
+        The options argument contains various bit settings that affect the com-
-        tion.  It  should  be  zero  if  no options are required. The available
+        pilation. It should be zero if no options are required.  The  available
-        options are described below. Some of them, in  particular,  those  that
+        options  are  described  below. Some of them, in particular, those that
-        are  compatible  with  Perl,  can also be set and unset from within the
+        are compatible with Perl, can also be set and  unset  from  within  the
-        pattern (see the detailed description  in  the  pcrepattern  documenta-
+        pattern  (see  the  detailed  description in the pcrepattern documenta-
-        tion).  For  these options, the contents of the options argument speci-
+        tion). For these options, the contents of the options  argument  speci-
-        fies their initial settings at the start of compilation and  execution.
+        fies  their initial settings at the start of compilation and execution.
-        The  PCRE_ANCHORED option can be set at the time of matching as well as
+        The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at  the  time
-        at compile time.
+        of matching as well as at compile time.
         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
-        if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
+        if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
         sets the variable pointed to by errptr to point to a textual error mes-
-        sage.  The  offset from the start of the pattern to the character where
+        sage. This is a static string that is part of the library. You must not
-        the error was discovered is  placed  in  the  variable  pointed  to  by
+        try to free it. The offset from the start of the pattern to the charac-
-        erroffset,  which  must  not  be  NULL. If it is, an immediate error is
+        ter where the error was discovered is placed in the variable pointed to
+        by  erroffset,  which must not be NULL. If it is, an immediate error is
         given.
         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-
-Line 926 
 COMPILING A PATTERN
+Line 1083 
 COMPILING A PATTERN
         If this bit is set, a dollar metacharacter in the pattern matches  only
         at  the  end  of the subject string. Without this option, a dollar also
-        matches immediately before the final character if it is a newline  (but
+        matches immediately before a newline at the end of the string (but  not
-        not  before  any  other  newlines).  The  PCRE_DOLLAR_ENDONLY option is
+        before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
-        ignored if PCRE_MULTILINE is set. There is no equivalent to this option
+        if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in
-        in Perl, and no way to set it within a pattern.
+        Perl, and no way to set it within a pattern.
           PCRE_DOTALL
         If this bit is set, a dot metacharater in the pattern matches all char-
-        acters, including newlines. Without it,  newlines  are  excluded.  This
+        acters, including those that indicate newline. Without it, a  dot  does
-        option  is equivalent to Perl's /s option, and it can be changed within
+        not  match  when  the  current position is at a newline. This option is
-        a pattern by a (?s) option setting.  A  negative  class  such  as  [^a]
+        equivalent to Perl's /s option, and it can be changed within a  pattern
-        always  matches a newline character, independent of the setting of this
+        by  a (?s) option setting. A negative class such as [^a] always matches
-        option.
+        newline characters, independent of the setting of this option.
+          PCRE_DUPNAMES
+        If this bit is set, names used to identify capturing  subpatterns  need
+        not be unique. This can be helpful for certain types of pattern when it
+        is known that only one instance of the named  subpattern  can  ever  be
+        matched.  There  are  more details of named subpatterns below; see also
+        the pcrepattern documentation.
           PCRE_EXTENDED
-Line 946 
 COMPILING A PATTERN
+Line 1111 
 COMPILING A PATTERN
         totally ignored except when escaped or inside a character class. White-
         space does not include the VT character (code 11). In addition, charac-
         ters between an unescaped # outside a character class and the next new-
-        line character, inclusive, are also  ignored.  This  is  equivalent  to
+        line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
-        Perl's  /x  option,  and  it  can be changed within a pattern by a (?x)
+        option,  and  it  can be changed within a pattern by a (?x) option set-
-        option setting.
+        ting.
         This option makes it possible to include  comments  inside  complicated
         patterns.   Note,  however,  that this applies only to data characters.
-Line 964 
 COMPILING A PATTERN
+Line 1129 
 COMPILING A PATTERN
         letter  that  has  no  special  meaning causes an error, thus reserving
         these combinations for future expansion. By  default,  as  in  Perl,  a
         backslash  followed by a letter with no special meaning is treated as a
-        literal. There are at present no  other  features  controlled  by  this
+        literal. (Perl can, however, be persuaded to give a warning for  this.)
-        option. It can also be set by a (?X) option setting within a pattern.
+        There  are  at  present no other features controlled by this option. It
+        can also be set by a (?X) option setting within a pattern.
           PCRE_FIRSTLINE
-        If  this  option  is  set,  an  unanchored pattern is required to match
+        If this option is set, an  unanchored  pattern  is  required  to  match
-        before or at the first newline character in the subject string,  though
+        before  or  at  the  first  newline  in  the subject string, though the
-        the matched text may continue over the newline.
+        matched text may continue over the newline.
           PCRE_MULTILINE
-        By  default,  PCRE  treats the subject string as consisting of a single
+        By default, PCRE treats the subject string as consisting  of  a  single
-        line of characters (even if it actually contains newlines). The  "start
+        line  of characters (even if it actually contains newlines). The "start
-        of  line"  metacharacter  (^)  matches only at the start of the string,
+        of line" metacharacter (^) matches only at the  start  of  the  string,
-        while the "end of line" metacharacter ($) matches only at  the  end  of
+        while  the  "end  of line" metacharacter ($) matches only at the end of
         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
         is set). This is the same as Perl.
-        When PCRE_MULTILINE it is set, the "start of line" and  "end  of  line"
+        When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"
-        constructs  match  immediately following or immediately before any new-
+        constructs match immediately following or immediately  before  internal
-        line in the subject string, respectively, as well as at the very  start
+        newlines  in  the  subject string, respectively, as well as at the very
-        and  end. This is equivalent to Perl's /m option, and it can be changed
+        start and end. This is equivalent to Perl's /m option, and  it  can  be
-        within a pattern by a (?m) option setting. If there are no "\n" charac-
+        changed within a pattern by a (?m) option setting. If there are no new-
-        ters  in  a  subject  string, or no occurrences of ^ or $ in a pattern,
+        lines in a subject string, or no occurrences of ^ or $  in  a  pattern,
         setting PCRE_MULTILINE has no effect.
+          PCRE_NEWLINE_CR
+          PCRE_NEWLINE_LF
+          PCRE_NEWLINE_CRLF
+          PCRE_NEWLINE_ANYCRLF
+          PCRE_NEWLINE_ANY
+        These  options  override the default newline definition that was chosen
+        when PCRE was built. Setting the first or the second specifies  that  a
+        newline  is  indicated  by a single character (CR or LF, respectively).
+        Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
+        two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
+        that any of the three preceding sequences should be recognized. Setting
+        PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
+        recognized. The Unicode newline sequences are the three just mentioned,
+        plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
+        U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
+        (paragraph  separator,  U+2029).  The  last  two are recognized only in
+        UTF-8 mode.
+        The newline setting in the  options  word  uses  three  bits  that  are
+        treated as a number, giving eight possibilities. Currently only six are
+        used (default plus the five values above). This means that if  you  set
+        more  than one newline option, the combination may or may not be sensi-
+        ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
+        PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
+        cause an error.
+        The only time that a line break is specially recognized when  compiling
+        a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
+        character class is encountered. This indicates  a  comment  that  lasts
+        until  after the next line break sequence. In other circumstances, line
+        break  sequences  are  treated  as  literal  data,   except   that   in
+        PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
+        and are therefore ignored.
+        The newline option that is set at compile time becomes the default that
+        is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
           PCRE_NO_AUTO_CAPTURE
         If this option is set, it disables the use of numbered capturing paren-
-Line 1031 
 COMPILATION ERROR CODES
+Line 1235 
 COMPILATION ERROR CODES
         The following table lists the error  codes  than  may  be  returned  by
         pcre_compile2(),  along with the error messages that may be returned by
-        both compiling functions.
+        both compiling functions. As PCRE has developed, some error codes  have
+        fallen out of use. To avoid confusion, they have not been re-used.
  no error
  \ at end of pattern
-Line 1043 
 COMPILATION ERROR CODES
+Line 1248 
 COMPILATION ERROR CODES
  invalid escape sequence in character class
  range out of order in character class
  nothing to repeat
- operand of unlimited repeat could match the empty string
+ [this code is not in use]
  internal error: unexpected repeat
  unrecognized character after (?
  POSIX named classes are supported only within a class
-Line 1052 
 COMPILATION ERROR CODES
+Line 1257 
 COMPILATION ERROR CODES
  erroffset passed as NULL
  unknown option bit(s) set
  missing ) after comment
- parentheses nested too deeply
+ [this code is not in use]
  regular expression too large
  failed to get memory
  unmatched parentheses
  internal error: code overflow
  unrecognized character after (?<
  lookbehind assertion is not fixed length
- malformed number after (?(
+ malformed number or name after (?(
  conditional group contains more than two branches
  assertion expected after (?(
- (?R or (?digits must be followed by )
+ (?R or (?[+-]digits must be followed by )
  unknown POSIX class name
  POSIX collating elements are not supported
  this version of PCRE is not compiled with PCRE_UTF8 support
- spare error
+ [this code is not in use]
  character value in \x{...} sequence is too large
  invalid condition (?(0)
  \C not allowed in lookbehind assertion
-Line 1075 
 COMPILATION ERROR CODES
+Line 1280 
 COMPILATION ERROR CODES
  closing ) for (?C expected
  recursive call could loop indefinitely
  unrecognized character after (?P
- syntax error after (?P
+ syntax error in subpattern name (missing terminator)
- two named groups have the same name
+ two named subpatterns have the same name
  invalid UTF-8 string
  support for \P, \p, and \X has not been compiled
  malformed \P or \p sequence
  unknown property name after \P or \p
+ subpattern name is too long (maximum 32 characters)
+ too many named subpatterns (maximum 10,000)
+ repeated subpattern is too long
+ octal value is greater than \377 (not in UTF-8 mode)
+ internal error: overran compiling workspace
+  internal  error:  previously-checked  referenced  subpattern not
+        found
+ DEFINE group contains more than one branch
+ repeating a DEFINE group is not allowed
+ inconsistent NEWLINE options"
+ \g is not followed by a braced name or an optionally braced
+                non-zero number
+ (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
  STUDYING A PATTERN
-Line 1111 
 STUDYING A PATTERN
+Line 1329 
 STUDYING A PATTERN
         The  third argument for pcre_study() is a pointer for an error message.
         If studying succeeds (even if no data is  returned),  the  variable  it
-        points  to  is set to NULL. Otherwise it points to a textual error mes-
+        points  to  is  set  to NULL. Otherwise it is set to point to a textual
-        sage. You should therefore test the error pointer for NULL after  call-
+        error message. This is a static string that is part of the library. You
-        ing pcre_study(), to be sure that it has run successfully.
+        must  not  try  to  free it. You should test the error pointer for NULL
+        after calling pcre_study(), to be sure that it has run successfully.
         This is a typical call to pcre_study():
-Line 1124 
 STUDYING A PATTERN
+Line 1343 
 STUDYING A PATTERN
             &error);        /* set to NULL or points to a message */
         At present, studying a pattern is useful only for non-anchored patterns
-        that do not have a single fixed starting character. A bitmap of  possi-
+        that  do not have a single fixed starting character. A bitmap of possi-
         ble starting bytes is created.
  LOCALE SUPPORT
-        PCRE  handles  caseless matching, and determines whether characters are
+        PCRE handles caseless matching, and determines whether  characters  are
-        letters digits, or whatever, by reference to a set of  tables,  indexed
+        letters,  digits, or whatever, by reference to a set of tables, indexed
-        by  character  value.  When running in UTF-8 mode, this applies only to
+        by character value. When running in UTF-8 mode, this  applies  only  to
-        characters with codes less than 128. Higher-valued  codes  never  match
+        characters  with  codes  less than 128. Higher-valued codes never match
-        escapes  such  as  \w or \d, but can be tested with \p if PCRE is built
+        escapes such as \w or \d, but can be tested with \p if  PCRE  is  built
-        with Unicode character property support.
+        with  Unicode  character property support. The use of locales with Uni-
+        code is discouraged. If you are handling characters with codes  greater
-        An internal set of tables is created in the default C locale when  PCRE
+        than  128, you should either use UTF-8 and Unicode, or use locales, but
-        is  built.  This  is  used when the final argument of pcre_compile() is
+        not try to mix the two.
-        NULL, and is sufficient for many applications. An  alternative  set  of
-        tables  can,  however, be supplied. These may be created in a different
+        PCRE contains an internal set of tables that are used  when  the  final
-        locale from the default. As more and more applications change to  using
+        argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
-        Unicode, the need for this locale support is expected to die away.
+        applications.  Normally, the internal tables recognize only ASCII char-
+        acters. However, when PCRE is built, it is possible to cause the inter-
-        External  tables  are  built by calling the pcre_maketables() function,
+        nal tables to be rebuilt in the default "C" locale of the local system,
-        which has no arguments, in the relevant locale. The result can then  be
+        which may cause them to be different.
-        passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For
-        example, to build and use tables that are appropriate  for  the  French
+        The  internal tables can always be overridden by tables supplied by the
-        locale  (where  accented  characters  with  values greater than 128 are
+        application that calls PCRE. These may be created in a different locale
+        from  the  default.  As more and more applications change to using Uni-
+        code, the need for this locale support is expected to die away.
+        External tables are built by calling  the  pcre_maketables()  function,
+        which  has no arguments, in the relevant locale. The result can then be
+        passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
+        example,  to  build  and use tables that are appropriate for the French
+        locale (where accented characters with  values  greater  than  128  are
         treated as letters), the following code could be used:
           setlocale(LC_CTYPE, "fr_FR");
           tables = pcre_maketables();
           re = pcre_compile(..., tables);
+        The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
+        if you are using Windows, the name for the French locale is "french".
         When pcre_maketables() runs, the tables are built  in  memory  that  is
         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
         that the memory containing the tables remains available for as long  as
-Line 1200 
 INFORMATION ABOUT A PATTERN
+Line 1430 
 INFORMATION ABOUT A PATTERN
         pattern:
           int rc;
-          unsigned long int length;
+          size_t length;
           rc = pcre_fullinfo(
             re,               /* result of pcre_compile() */
             pe,               /* result of pcre_study(), or NULL */
-Line 1232 
 INFORMATION ABOUT A PATTERN
+Line 1462 
 INFORMATION ABOUT A PATTERN
           PCRE_INFO_FIRSTBYTE
         Return  information  about  the first byte of any matched string, for a
-        non-anchored   pattern.   (This    option    used    to    be    called
+        non-anchored pattern. The fourth argument should point to an int  vari-
-        PCRE_INFO_FIRSTCHAR;  the  old  name  is still recognized for backwards
+        able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
-        compatibility.)
+        is still recognized for backwards compatibility.)
         If there is a fixed first byte, for example, from  a  pattern  such  as
-        (cat|cow|coyote),  it  is  returned in the integer pointed to by where.
+        (cat|cow|coyote), its value is returned. Otherwise, if either
-        Otherwise, if either
-        (a) the pattern was compiled with the PCRE_MULTILINE option, and  every
+        (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
         branch starts with "^", or
         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
         set (if it were set, the pattern would be anchored),
-        -1 is returned, indicating that the pattern matches only at  the  start
+        -1  is  returned, indicating that the pattern matches only at the start
-        of  a  subject string or after any newline within the string. Otherwise
+        of a subject string or after any newline within the  string.  Otherwise
         -2 is returned. For anchored patterns, -2 is returned.
           PCRE_INFO_FIRSTTABLE
-        If the pattern was studied, and this resulted in the construction of  a
+        If  the pattern was studied, and this resulted in the construction of a
 -bit table indicating a fixed set of bytes for the first byte in any
-        matching string, a pointer to the table is returned. Otherwise NULL  is
+        matching  string, a pointer to the table is returned. Otherwise NULL is
-        returned.  The fourth argument should point to an unsigned char * vari-
+        returned. The fourth argument should point to an unsigned char *  vari-
         able.
+          PCRE_INFO_JCHANGED
+        Return  1  if the (?J) option setting is used in the pattern, otherwise
+. The fourth argument should point to an int variable. The (?J) inter-
+        nal option setting changes the local PCRE_DUPNAMES option.
           PCRE_INFO_LASTLITERAL
-        Return the value of the rightmost literal byte that must exist  in  any
+        Return  the  value of the rightmost literal byte that must exist in any
-        matched  string,  other  than  at  its  start,  if such a byte has been
+        matched string, other than at its  start,  if  such  a  byte  has  been
         recorded. The fourth argument should point to an int variable. If there
-        is  no such byte, -1 is returned. For anchored patterns, a last literal
+        is no such byte, -1 is returned. For anchored patterns, a last  literal
-        byte is recorded only if it follows something of variable  length.  For
+        byte  is  recorded only if it follows something of variable length. For
         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
         /^a\dz\d/ the returned value is -1.
-Line 1272 
 INFORMATION ABOUT A PATTERN
+Line 1507 
 INFORMATION ABOUT A PATTERN
           PCRE_INFO_NAMEENTRYSIZE
           PCRE_INFO_NAMETABLE
-        PCRE supports the use of named as well as numbered capturing  parenthe-
+        PCRE  supports the use of named as well as numbered capturing parenthe-
-        ses.  The names are just an additional way of identifying the parenthe-
+        ses. The names are just an additional way of identifying the  parenthe-
-        ses,  which  still  acquire  numbers.  A  convenience  function  called
+        ses, which still acquire numbers. Several convenience functions such as
-        pcre_get_named_substring()  is  provided  for  extracting an individual
+        pcre_get_named_substring() are provided for  extracting  captured  sub-
-        captured substring by name. It is also possible  to  extract  the  data
+        strings  by  name. It is also possible to extract the data directly, by
-        directly,  by  first converting the name to a number in order to access
+        first converting the name to a number in order to  access  the  correct
-        the correct pointers in the output vector (described  with  pcre_exec()
+        pointers in the output vector (described with pcre_exec() below). To do
-        below).  To  do the conversion, you need to use the name-to-number map,
+        the conversion, you need  to  use  the  name-to-number  map,  which  is
-        which is described by these three values.
+        described by these three values.
         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
-        of each entry; both of these  return  an  int  value.  The  entry  size
+        of  each  entry;  both  of  these  return  an int value. The entry size
-        depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
+        depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
-        a pointer to the first entry of the table  (a  pointer  to  char).  The
+        a  pointer  to  the  first  entry of the table (a pointer to char). The
         first two bytes of each entry are the number of the capturing parenthe-
-        sis, most significant byte first. The rest of the entry is  the  corre-
+        sis,  most  significant byte first. The rest of the entry is the corre-
-        sponding  name,  zero  terminated. The names are in alphabetical order.
+        sponding name, zero terminated. The names are  in  alphabetical  order.
-        For example, consider the following pattern  (assume  PCRE_EXTENDED  is
+        When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
-        set, so white space - including newlines - is ignored):
+        theses numbers. For example, consider  the  following  pattern  (assume
+        PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
+        ignored):
-          (?P<date> (?P<year>(\d\d)?\d\d) -
+          (?<date> (?<year>(\d\d)?\d\d) -
-          (?P<month>\d\d) - (?P<day>\d\d) )
+          (?<month>\d\d) - (?<day>\d\d) )
-        There  are  four  named subpatterns, so the table has four entries, and
+        There are four named subpatterns, so the table has  four  entries,  and
-        each entry in the table is eight bytes long. The table is  as  follows,
+        each  entry  in the table is eight bytes long. The table is as follows,
         with non-printing bytes shows in hexadecimal, and undefined bytes shown
         as ??:
-Line 1306 
 INFORMATION ABOUT A PATTERN
+Line 1543 
 INFORMATION ABOUT A PATTERN
 04 m  o  n  t  h  00
 02 y  e  a  r  00 ??
-        When writing code to extract data  from  named  subpatterns  using  the
+        When  writing  code  to  extract  data from named subpatterns using the
-        name-to-number map, remember that the length of each entry is likely to
+        name-to-number map, remember that the length of the entries  is  likely
-        be different for each compiled pattern.
+        to be different for each compiled pattern.
+          PCRE_INFO_OKPARTIAL
+        Return  1 if the pattern can be used for partial matching, otherwise 0.
+        The fourth argument should point to an int  variable.  The  pcrepartial
+        documentation  lists  the restrictions that apply to patterns when par-
+        tial matching is used.
           PCRE_INFO_OPTIONS
-Line 1428 
 MATCHING A PATTERN: THE TRADITIONAL FUNC
+Line 1672 
 MATCHING A PATTERN: THE TRADITIONAL FUNC
         If the extra argument is not NULL, it must point to a  pcre_extra  data
         block.  The pcre_study() function returns such a block (when it doesn't
         return NULL), but you can also create one for yourself, and pass  addi-
-        tional  information in it. The fields in a pcre_extra block are as fol-
+        tional  information  in it. The pcre_extra block contains the following
-        lows:
+        fields (not necessarily in this order):
           unsigned long int flags;
           void *study_data;
           unsigned long int match_limit;
+          unsigned long int match_limit_recursion;
           void *callout_data;
           const unsigned char *tables;
-Line 1442 
 MATCHING A PATTERN: THE TRADITIONAL FUNC
+Line 1687 
 MATCHING A PATTERN: THE TRADITIONAL FUNC
           PCRE_EXTRA_STUDY_DATA
           PCRE_EXTRA_MATCH_LIMIT
+          PCRE_EXTRA_MATCH_LIMIT_RECURSION
           PCRE_EXTRA_CALLOUT_DATA
           PCRE_EXTRA_TABLES
-Line 1458 
 MATCHING A PATTERN: THE TRADITIONAL FUNC
+Line 1704 
 MATCHING A PATTERN: THE TRADITIONAL FUNC
         repeats.
         Internally,  PCRE uses a function called match() which it calls repeat-
-        edly (sometimes recursively). The limit is imposed  on  the  number  of
+        edly (sometimes recursively). The limit set by match_limit  is  imposed
-        times  this  function is called during a match, which has the effect of
+        on  the  number  of times this function is called during a match, which
-        limiting the amount of recursion and backtracking that can take  place.
+        has the effect of limiting the amount of  backtracking  that  can  take
-        For patterns that are not anchored, the count starts from zero for each
+        place. For patterns that are not anchored, the count restarts from zero
-        position in the subject string.
+        for each position in the subject string.
-        The default limit for the library can be set when PCRE  is  built;  the
+        The default value for the limit can be set  when  PCRE  is  built;  the
         default  default  is 10 million, which handles all but the most extreme
-        cases. You can reduce  the  default  by  suppling  pcre_exec()  with  a
+        cases. You can override the default  by  suppling  pcre_exec()  with  a
-        pcre_extra  block  in  which match_limit is set to a smaller value, and
+        pcre_extra     block    in    which    match_limit    is    set,    and
         PCRE_EXTRA_MATCH_LIMIT is set in the  flags  field.  If  the  limit  is
         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
+        The  match_limit_recursion field is similar to match_limit, but instead
+        of limiting the total number of times that match() is called, it limits
+        the  depth  of  recursion. The recursion depth is a smaller number than
+        the total number of calls, because not all calls to match() are  recur-
+        sive.  This limit is of use only if it is set smaller than match_limit.
+        Limiting the recursion depth limits the amount of  stack  that  can  be
+        used, or, when PCRE has been compiled to use memory on the heap instead
+        of the stack, the amount of heap memory that can be used.
+        The default value for match_limit_recursion can be  set  when  PCRE  is
+        built;  the  default  default  is  the  same  value  as the default for
+        match_limit. You can override the default by suppling pcre_exec()  with
+        a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and
+        PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the
+        limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
         The  pcre_callout  field is used in conjunction with the "callout" fea-
         ture, which is described in the pcrecallout documentation.
-Line 1488 
 MATCHING A PATTERN: THE TRADITIONAL FUNC
+Line 1751 
 MATCHING A PATTERN: THE TRADITIONAL FUNC
     Option bits for pcre_exec()
         The  unused  bits of the options argument for pcre_exec() must be zero.
-        The  only  bits  that  may  be  set  are  PCRE_ANCHORED,   PCRE_NOTBOL,
+        The only bits that may  be  set  are  PCRE_ANCHORED,  PCRE_NEWLINE_xxx,
-        PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.
+        PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
+        PCRE_PARTIAL.
           PCRE_ANCHORED
-        The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
+        The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first
-        matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
+        matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or
-        turned  out to be anchored by virtue of its contents, it cannot be made
+        turned out to be anchored by virtue of its contents, it cannot be  made
         unachored at matching time.
+          PCRE_NEWLINE_CR
+          PCRE_NEWLINE_LF
+          PCRE_NEWLINE_CRLF
+          PCRE_NEWLINE_ANYCRLF
+          PCRE_NEWLINE_ANY
+        These  options  override  the  newline  definition  that  was chosen or
+        defaulted when the pattern was compiled. For details, see the  descrip-
+        tion  of  pcre_compile()  above.  During  matching,  the newline choice
+        affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
+        ters.  It may also alter the way the match position is advanced after a
+        match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,
+        PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY is set, and a match attempt
+        fails when the current position is at a CRLF sequence, the match  posi-
+        tion  is  advanced by two characters instead of one, in other words, to
+        after the CRLF.
           PCRE_NOTBOL
         This option specifies that first character of the subject string is not
-Line 1633 
 MATCHING A PATTERN: THE TRADITIONAL FUNC
+Line 1914 
 MATCHING A PATTERN: THE TRADITIONAL FUNC
         after the end of a substring. The  first  pair,  ovector[0]  and  ovec-
         tor[1],  identify  the  portion  of  the  subject string matched by the
         entire pattern. The next pair is used for the first  capturing  subpat-
-        tern,  and  so  on.  The value returned by pcre_exec() is the number of
+        tern, and so on. The value returned by pcre_exec() is one more than the
-        pairs that have been set. If there are no  capturing  subpatterns,  the
+        highest numbered pair that has been set. For example, if two substrings
-        return  value  from  a  successful match is 1, indicating that just the
+        have  been captured, the returned value is 3. If there are no capturing
-        first pair of offsets has been set.
+        subpatterns, the return value from a successful match is 1,  indicating
+        that just the first pair of offsets has been set.
-        Some convenience functions are provided  for  extracting  the  captured
-        substrings  as  separate  strings. These are described in the following
-        section.
-        It is possible for an capturing subpattern number  n+1  to  match  some
-        part  of  the  subject  when subpattern n has not been used at all. For
-        example, if the string "abc" is matched against the pattern (a|(z))(bc)
-        subpatterns  1 and 3 are matched, but 2 is not. When this happens, both
-        offset values corresponding to the unused subpattern are set to -1.
         If a capturing subpattern is matched repeatedly, it is the last portion
         of the string that it matched that is returned.
-        If  the vector is too small to hold all the captured substring offsets,
+        If the vector is too small to hold all the captured substring  offsets,
         it is used as far as possible (up to two-thirds of its length), and the
-        function  returns a value of zero. In particular, if the substring off-
+        function returns a value of zero. In particular, if the substring  off-
         sets are not of interest, pcre_exec() may be called with ovector passed
-        as  NULL  and  ovecsize  as zero. However, if the pattern contains back
+        as NULL and ovecsize as zero. However, if  the  pattern  contains  back
-        references and the ovector is not big enough to  remember  the  related
+        references  and  the  ovector is not big enough to remember the related
-        substrings,  PCRE has to get additional memory for use during matching.
+        substrings, PCRE has to get additional memory for use during  matching.
         Thus it is usually advisable to supply an ovector.
-        Note that pcre_info() can be used to find out how many  capturing  sub-
+        The  pcre_info()  function  can  be used to find out how many capturing
-        patterns there are in a compiled pattern. The smallest size for ovector
+        subpatterns there are in a compiled  pattern.  The  smallest  size  for
-        that will allow for n captured substrings, in addition to  the  offsets
+        ovector  that  will allow for n captured substrings, in addition to the
-        of the substring matched by the whole pattern, is (n+1)*3.
+        offsets of the substring matched by the whole pattern, is (n+1)*3.
+        It is possible for capturing subpattern number n+1 to match  some  part
+        of the subject when subpattern n has not been used at all. For example,
+        if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
+        return from the function is 4, and subpatterns 1 and 3 are matched, but
+is not. When this happens, both values in  the  offset  pairs  corre-
+        sponding to unused subpatterns are set to -1.
+        Offset  values  that correspond to unused subpatterns at the end of the
+        expression are also set to -1. For example,  if  the  string  "abc"  is
+        matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
+        matched. The return from the function is 2, because  the  highest  used
+        capturing subpattern number is 1. However, you can refer to the offsets
+        for the second and third capturing subpatterns if  you  wish  (assuming
+        the vector is large enough, of course).
-    Return values from pcre_exec()
+        Some  convenience  functions  are  provided for extracting the captured
+        substrings as separate strings. These are described below.
-        If  pcre_exec()  fails, it returns a negative number. The following are
+    Error return values from pcre_exec()
+        If pcre_exec() fails, it returns a negative number. The  following  are
         defined in the header file:
           PCRE_ERROR_NOMATCH        (-1)
-Line 1676 
 MATCHING A PATTERN: THE TRADITIONAL FUNC
+Line 1966 
 MATCHING A PATTERN: THE TRADITIONAL FUNC
           PCRE_ERROR_NULL           (-2)
-        Either code or subject was passed as NULL,  or  ovector  was  NULL  and
+        Either  code  or  subject  was  passed as NULL, or ovector was NULL and
         ovecsize was not zero.
           PCRE_ERROR_BADOPTION      (-3)
-Line 1685 
 MATCHING A PATTERN: THE TRADITIONAL FUNC
+Line 1975 
 MATCHING A PATTERN: THE TRADITIONAL FUNC
           PCRE_ERROR_BADMAGIC       (-4)
-        PCRE  stores a 4-byte "magic number" at the start of the compiled code,
+        PCRE stores a 4-byte "magic number" at the start of the compiled  code,
         to catch the case when it is passed a junk pointer and to detect when a
         pattern that was compiled in an environment of one endianness is run in
-        an environment with the other endianness. This is the error  that  PCRE
+        an  environment  with the other endianness. This is the error that PCRE
         gives when the magic number is not present.
-          PCRE_ERROR_UNKNOWN_NODE   (-5)
+          PCRE_ERROR_UNKNOWN_OPCODE (-5)
         While running the pattern match, an unknown item was encountered in the
-        compiled pattern. This error could be caused by a bug  in  PCRE  or  by
+        compiled  pattern.  This  error  could be caused by a bug in PCRE or by
         overwriting of the compiled pattern.
           PCRE_ERROR_NOMEMORY       (-6)
-        If  a  pattern contains back references, but the ovector that is passed
+        If a pattern contains back references, but the ovector that  is  passed
         to pcre_exec() is not big enough to remember the referenced substrings,
-        PCRE  gets  a  block of memory at the start of matching to use for this
+        PCRE gets a block of memory at the start of matching to  use  for  this
-        purpose. If the call via pcre_malloc() fails, this error is given.  The
+        purpose.  If the call via pcre_malloc() fails, this error is given. The
         memory is automatically freed at the end of matching.
           PCRE_ERROR_NOSUBSTRING    (-7)
-        This  error is used by the pcre_copy_substring(), pcre_get_substring(),
+        This error is used by the pcre_copy_substring(),  pcre_get_substring(),
         and  pcre_get_substring_list()  functions  (see  below).  It  is  never
         returned by pcre_exec().
           PCRE_ERROR_MATCHLIMIT     (-8)
-        The  recursion  and backtracking limit, as specified by the match_limit
+        The backtracking limit, as specified by  the  match_limit  field  in  a
-        field in a pcre_extra structure (or defaulted)  was  reached.  See  the
+        pcre_extra  structure  (or  defaulted) was reached. See the description
-        description above.
+        above.
           PCRE_ERROR_CALLOUT        (-9)
         This error is never generated by pcre_exec() itself. It is provided for
-        use by callout functions that want to yield a distinctive  error  code.
+        use  by  callout functions that want to yield a distinctive error code.
         See the pcrecallout documentation for details.
           PCRE_ERROR_BADUTF8        (-10)
-        A  string  that contains an invalid UTF-8 byte sequence was passed as a
+        A string that contains an invalid UTF-8 byte sequence was passed  as  a
         subject.
           PCRE_ERROR_BADUTF8_OFFSET (-11)
         The UTF-8 byte sequence that was passed as a subject was valid, but the
-        value  of startoffset did not point to the beginning of a UTF-8 charac-
+        value of startoffset did not point to the beginning of a UTF-8  charac-
         ter.
           PCRE_ERROR_PARTIAL        (-12)
-        The subject string did not match, but it did match partially.  See  the
+        The  subject  string did not match, but it did match partially. See the
         pcrepartial documentation for details of partial matching.
           PCRE_ERROR_BADPARTIAL     (-13)
-        The  PCRE_PARTIAL  option  was  used with a compiled pattern containing
+        The PCRE_PARTIAL option was used with  a  compiled  pattern  containing
-        items that are not supported for partial matching. See the  pcrepartial
+        items  that are not supported for partial matching. See the pcrepartial
         documentation for details of partial matching.
           PCRE_ERROR_INTERNAL       (-14)
-        An  unexpected  internal error has occurred. This error could be caused
+        An unexpected internal error has occurred. This error could  be  caused
         by a bug in PCRE or by overwriting of the compiled pattern.
           PCRE_ERROR_BADCOUNT       (-15)
-        This error is given if the value of the ovecsize argument is  negative.
+        This  error is given if the value of the ovecsize argument is negative.
+          PCRE_ERROR_RECURSIONLIMIT (-21)
+        The internal recursion limit, as specified by the match_limit_recursion
+        field  in  a  pcre_extra  structure (or defaulted) was reached. See the
+        description above.
+          PCRE_ERROR_NULLWSLIMIT    (-22)
+        When a group that can match an empty  substring  is  repeated  with  an
+        unbounded  upper  limit, the subject position at the start of the group
+        must be remembered, so that a test for an empty string can be made when
+        the  end  of the group is reached. Some workspace is required for this;
+        if it runs out, this error is given.
+          PCRE_ERROR_BADNEWLINE     (-23)
+        An invalid combination of PCRE_NEWLINE_xxx options was given.
+        Error numbers -16 to -20 are not used by pcre_exec().
  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
-Line 1768 
 EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
+Line 2078 
 EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
         int pcre_get_substring_list(const char *subject,
              int *ovector, int stringcount, const char ***listptr);
-        Captured  substrings  can  be  accessed  directly  by using the offsets
+        Captured substrings can be  accessed  directly  by  using  the  offsets
-        returned by pcre_exec() in  ovector.  For  convenience,  the  functions
+        returned  by  pcre_exec()  in  ovector.  For convenience, the functions
         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
-        string_list() are provided for extracting captured substrings  as  new,
+        string_list()  are  provided for extracting captured substrings as new,
-        separate,  zero-terminated strings. These functions identify substrings
+        separate, zero-terminated strings. These functions identify  substrings
-        by number. The next section describes functions  for  extracting  named
+        by  number.  The  next section describes functions for extracting named
-        substrings.  A  substring  that  contains  a  binary  zero is correctly
+        substrings.
-        extracted and has a further zero added on the end, but  the  result  is
-        not, of course, a C string.
+        A substring that contains a binary zero is correctly extracted and  has
+        a  further zero added on the end, but the result is not, of course, a C
+        string.  However, you can process such a string  by  referring  to  the
+        length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
+        string().  Unfortunately, the interface to pcre_get_substring_list() is
+        not  adequate for handling strings containing binary zeros, because the
+        end of the final string is not independently indicated.
-        The  first  three  arguments  are the same for all three of these func-
+        The first three arguments are the same for all  three  of  these  func-
-        tions: subject is the subject string that has  just  been  successfully
+        tions:  subject  is  the subject string that has just been successfully
         matched, ovector is a pointer to the vector of integer offsets that was
         passed to pcre_exec(), and stringcount is the number of substrings that
-        were  captured  by  the match, including the substring that matched the
+        were captured by the match, including the substring  that  matched  the
         entire regular expression. This is the value returned by pcre_exec() if
-        it  is greater than zero. If pcre_exec() returned zero, indicating that
+        it is greater than zero. If pcre_exec() returned zero, indicating  that
-        it ran out of space in ovector, the value passed as stringcount  should
+        it  ran out of space in ovector, the value passed as stringcount should
         be the number of elements in the vector divided by three.
-        The  functions pcre_copy_substring() and pcre_get_substring() extract a
+        The functions pcre_copy_substring() and pcre_get_substring() extract  a
-        single substring, whose number is given as  stringnumber.  A  value  of
+        single  substring,  whose  number  is given as stringnumber. A value of
-        zero  extracts  the  substring that matched the entire pattern, whereas
+        zero extracts the substring that matched the  entire  pattern,  whereas
-        higher values  extract  the  captured  substrings.  For  pcre_copy_sub-
+        higher  values  extract  the  captured  substrings.  For pcre_copy_sub-
-        string(),  the  string  is  placed  in buffer, whose length is given by
+        string(), the string is placed in buffer,  whose  length  is  given  by
-        buffersize, while for pcre_get_substring() a new  block  of  memory  is
+        buffersize,  while  for  pcre_get_substring()  a new block of memory is
-        obtained  via  pcre_malloc,  and its address is returned via stringptr.
+        obtained via pcre_malloc, and its address is  returned  via  stringptr.
-        The yield of the function is the length of the  string,  not  including
+        The  yield  of  the function is the length of the string, not including
-        the terminating zero, or one of
+        the terminating zero, or one of these error codes:
           PCRE_ERROR_NOMEMORY       (-6)
-        The  buffer  was too small for pcre_copy_substring(), or the attempt to
+        The buffer was too small for pcre_copy_substring(), or the  attempt  to
         get memory failed for pcre_get_substring().
           PCRE_ERROR_NOSUBSTRING    (-7)
         There is no substring whose number is stringnumber.
-        The pcre_get_substring_list()  function  extracts  all  available  sub-
+        The  pcre_get_substring_list()  function  extracts  all  available sub-
-        strings  and  builds  a list of pointers to them. All this is done in a
+        strings and builds a list of pointers to them. All this is  done  in  a
         single block of memory that is obtained via pcre_malloc. The address of
-        the  memory  block  is returned via listptr, which is also the start of
+        the memory block is returned via listptr, which is also  the  start  of
-        the list of string pointers. The end of the list is marked  by  a  NULL
+        the  list  of  string pointers. The end of the list is marked by a NULL
-        pointer. The yield of the function is zero if all went well, or
+        pointer. The yield of the function is zero if all  went  well,  or  the
+        error code
           PCRE_ERROR_NOMEMORY       (-6)
-Line 1831 
 EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
+Line 2148 
 EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
         tively.  They  do  nothing  more  than  call the function pointed to by
         pcre_free, which of course could be called directly from a  C  program.
         However,  PCRE is used in some situations where it is linked via a spe-
-        cial  interface  to  another  programming  language  which  cannot  use
+        cial  interface  to  another  programming  language  that  cannot   use
         pcre_free  directly;  it is for these cases that the functions are pro-
         vided.
-Line 1854 
 EXTRACTING CAPTURED SUBSTRINGS BY NAME
+Line 2171 
 EXTRACTING CAPTURED SUBSTRINGS BY NAME
         To extract a substring by name, you first have to find associated  num-
         ber.  For example, for this pattern
-          (a+)b(?P<xxx>\d+)...
+          (a+)b(?<xxx>\d+)...
-        the number of the subpattern called "xxx" is 2. You can find the number
+        the number of the subpattern called "xxx" is 2. If the name is known to
-        from the name by calling pcre_get_stringnumber(). The first argument is
+        be unique (PCRE_DUPNAMES was not set), you can find the number from the
-        the  compiled  pattern,  and  the  second is the name. The yield of the
+        name by calling pcre_get_stringnumber(). The first argument is the com-
-        function is the subpattern number, or  PCRE_ERROR_NOSUBSTRING  (-7)  if
+        piled pattern, and the second is the name. The yield of the function is
-        there is no subpattern of that name.
+        the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
+        subpattern of that name.
         Given the number, you can extract the substring directly, or use one of
         the functions described in the previous section. For convenience, there
         are also two functions that do the whole job.
-        Most    of    the    arguments   of   pcre_copy_named_substring()   and
+        Most   of   the   arguments    of    pcre_copy_named_substring()    and
-        pcre_get_named_substring() are the same  as  those  for  the  similarly
+        pcre_get_named_substring()  are  the  same  as  those for the similarly
-        named  functions  that extract by number. As these are described in the
+        named functions that extract by number. As these are described  in  the
-        previous section, they are not re-described here. There  are  just  two
+        previous  section,  they  are not re-described here. There are just two
         differences:
-        First,  instead  of a substring number, a substring name is given. Sec-
+        First, instead of a substring number, a substring name is  given.  Sec-
         ond, there is an extra argument, given at the start, which is a pointer
-        to  the compiled pattern. This is needed in order to gain access to the
+        to the compiled pattern. This is needed in order to gain access to  the
         name-to-number translation table.
-        These functions call pcre_get_stringnumber(), and if it succeeds,  they
+        These  functions call pcre_get_stringnumber(), and if it succeeds, they
-        then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
+        then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
-        ate.
+        ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
+        behaviour may not be what you want (see the next section).
+ DUPLICATE SUBPATTERN NAMES
+        int pcre_get_stringtable_entries(const pcre *code,
+             const char *name, char **first, char **last);
+        When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
+        subpatterns  are  not  required  to  be unique. Normally, patterns with
+        duplicate names are such that in any one match, only one of  the  named
+        subpatterns  participates. An example is shown in the pcrepattern docu-
+        mentation. When duplicates are present, pcre_copy_named_substring() and
+        pcre_get_named_substring()  return the first substring corresponding to
+        the given name that is set.  If  none  are  set,  an  empty  string  is
+        returned.  The pcre_get_stringnumber() function returns one of the num-
+        bers that are associated with the name, but it is not defined which  it
+        is.
+        If  you want to get full details of all captured substrings for a given
+        name, you must use  the  pcre_get_stringtable_entries()  function.  The
+        first argument is the compiled pattern, and the second is the name. The
+        third and fourth are pointers to variables which  are  updated  by  the
+        function. After it has run, they point to the first and last entries in
+        the name-to-number table  for  the  given  name.  The  function  itself
+        returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
+        there are none. The format of the table is described above in the  sec-
+        tion  entitled  Information  about  a  pattern.  Given all the relevant
+        entries for the name, you can extract each of their numbers, and  hence
+        the captured data, if any.
  FINDING ALL POSSIBLE MATCHES
-        The traditional matching function uses a  similar  algorithm  to  Perl,
+        The  traditional  matching  function  uses a similar algorithm to Perl,
         which stops when it finds the first match, starting at a given point in
-        the subject. If you want to find all possible matches, or  the  longest
+        the  subject.  If you want to find all possible matches, or the longest
-        possible  match,  consider using the alternative matching function (see
+        possible match, consider using the alternative matching  function  (see
-        below) instead. If you cannot use the alternative function,  but  still
+        below)  instead.  If you cannot use the alternative function, but still
-        need  to  find all possible matches, you can kludge it up by making use
+        need to find all possible matches, you can kludge it up by  making  use
         of the callout facility, which is described in the pcrecallout documen-
         tation.
         What you have to do is to insert a callout right at the end of the pat-
-        tern.  When your callout function is called, extract and save the  cur-
+        tern.   When your callout function is called, extract and save the cur-
-        rent  matched  substring.  Then  return  1, which forces pcre_exec() to
+        rent matched substring. Then return  1,  which  forces  pcre_exec()  to
-        backtrack and try other alternatives. Ultimately, when it runs  out  of
+        backtrack  and  try other alternatives. Ultimately, when it runs out of
         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
-Line 1907 
 MATCHING A PATTERN: THE ALTERNATIVE FUNC
+Line 2255 
 MATCHING A PATTERN: THE ALTERNATIVE FUNC
              int options, int *ovector, int ovecsize,
              int *workspace, int wscount);
-        The  function  pcre_dfa_exec()  is  called  to  match  a subject string
+        The function pcre_dfa_exec()  is  called  to  match  a  subject  string
-        against a compiled pattern, using a "DFA" matching algorithm. This  has
+        against  a  compiled pattern, using a matching algorithm that scans the
-        different  characteristics to the normal algorithm, and is not compati-
+        subject string just once, and does not backtrack.  This  has  different
-        ble with Perl. Some of the features of PCRE patterns are not supported.
+        characteristics  to  the  normal  algorithm, and is not compatible with
-        Nevertheless, there are times when this kind of matching can be useful.
+        Perl. Some of the features of PCRE patterns are not  supported.  Never-
-        For a discussion of the two matching algorithms, see  the  pcrematching
+        theless,  there are times when this kind of matching can be useful. For
-        documentation.
+        a discussion of the two matching algorithms, see the pcrematching docu-
+        mentation.
         The  arguments  for  the  pcre_dfa_exec()  function are the same as for
         pcre_exec(), plus two extras. The ovector argument is used in a differ-
-Line 1925 
 MATCHING A PATTERN: THE ALTERNATIVE FUNC
+Line 2274 
 MATCHING A PATTERN: THE ALTERNATIVE FUNC
         workspace vector should contain at least 20 elements. It  is  used  for
         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
         workspace will be needed for patterns and subjects where  there  are  a
-        lot of possible matches.
+        lot of potential matches.
-        Here is an example of a simple call to pcre_exec():
+        Here is an example of a simple call to pcre_dfa_exec():
           int rc;
           int ovector[10];
           int wspace[20];
-          rc = pcre_exec(
+          rc = pcre_dfa_exec(
             re,             /* result of pcre_compile() */
             NULL,           /* we didn't study the pattern */
             "some string",  /* the subject string */
-Line 1947 
 MATCHING A PATTERN: THE ALTERNATIVE FUNC
+Line 2296 
 MATCHING A PATTERN: THE ALTERNATIVE FUNC
     Option bits for pcre_dfa_exec()
         The  unused  bits  of  the options argument for pcre_dfa_exec() must be
-        zero. The only bits that may be  set  are  PCRE_ANCHORED,  PCRE_NOTBOL,
+        zero. The only bits  that  may  be  set  are  PCRE_ANCHORED,  PCRE_NEW-
-        PCRE_NOTEOL,     PCRE_NOTEMPTY,    PCRE_NO_UTF8_CHECK,    PCRE_PARTIAL,
+        LINE_xxx,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,
-        PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All  but  the  last  three  of
+        PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
-        these  are  the  same  as  for pcre_exec(), so their description is not
+        three of these are the same as for pcre_exec(), so their description is
-        repeated here.
+        not repeated here.
           PCRE_PARTIAL
-Line 1966 
 MATCHING A PATTERN: THE ALTERNATIVE FUNC
+Line 2315 
 MATCHING A PATTERN: THE ALTERNATIVE FUNC
           PCRE_DFA_SHORTEST
         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
-        stop  as  soon  as  it  has found one match. Because of the way the DFA
+        stop as soon as it has found one match. Because of the way the alterna-
-        algorithm works, this is necessarily the shortest possible match at the
+        tive algorithm works, this is necessarily the shortest  possible  match
-        first possible matching point in the subject string.
+        at the first possible matching point in the subject string.
           PCRE_DFA_RESTART
-Line 2004 
 MATCHING A PATTERN: THE ALTERNATIVE FUNC
+Line 2353 
 MATCHING A PATTERN: THE ALTERNATIVE FUNC
         On success, the yield of the function is a number  greater  than  zero,
         which  is  the  number of matched substrings. The substrings themselves
         are returned in ovector. Each string uses two elements;  the  first  is
-        the  offset  to the start, and the second is the offset to the end. All
+        the  offset  to  the start, and the second is the offset to the end. In
-        the strings have the same start offset. (Space could have been saved by
+        fact, all the strings have the same start  offset.  (Space  could  have
-        giving  this only once, but it was decided to retain some compatibility
+        been  saved by giving this only once, but it was decided to retain some
-        with the way pcre_exec() returns data, even though the meaning  of  the
+        compatibility with the way pcre_exec() returns data,  even  though  the
-        strings is different.)
+        meaning of the strings is different.)
         The strings are returned in reverse order of length; that is, the long-
         est matching string is given first. If there were too many  matches  to
-Line 2030 
 MATCHING A PATTERN: THE ALTERNATIVE FUNC
+Line 2379 
 MATCHING A PATTERN: THE ALTERNATIVE FUNC
           PCRE_ERROR_DFA_UCOND      (-17)
-        This  return is given if pcre_dfa_exec() encounters a condition item in
+        This  return  is  given  if pcre_dfa_exec() encounters a condition item
-        a pattern that uses a back reference for the  condition.  This  is  not
+        that uses a back reference for the condition, or a test  for  recursion
-        supported.
+        in a specific group. These are not supported.
           PCRE_ERROR_DFA_UMLIMIT    (-18)
-Line 2052 
 MATCHING A PATTERN: THE ALTERNATIVE FUNC
+Line 2401 
 MATCHING A PATTERN: THE ALTERNATIVE FUNC
         This error is given if the output vector  is  not  large  enough.  This
         should be extremely rare, as a vector of size 1000 is used.
- Last updated: 16 May 2005
- Copyright (c) 1997-2005 University of Cambridge.
+ SEE ALSO
+        pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
+        tial(3), pcreposix(3), pcreprecompile(3), pcresample(3),  pcrestack(3).
+ AUTHOR
+        Philip Hazel
+        University Computing Service
+        Cambridge CB2 3QH, England.
+ REVISION
+        Last updated: 13 June 2007
+        Copyright (c) 1997-2007 University of Cambridge.
  ------------------------------------------------------------------------------
-Line 2080 
 PCRE CALLOUTS
+Line 2445 
 PCRE CALLOUTS
         default value is zero.  For  example,  this  pattern  has  two  callout
         points:
-          (?C1)eabc(?C2)def
+          (?C1)abc(?C2)def
         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
         called, PCRE automatically  inserts  callouts,  all  with  number  255,
-Line 2155 
 THE CALLOUT INTERFACE
+Line 2520 
 THE CALLOUT INTERFACE
         The subject and subject_length fields contain copies of the values that
         were passed to pcre_exec().
-        The start_match field contains the offset within the subject  at  which
+        The start_match field normally contains the offset within  the  subject
-        the  current match attempt started. If the pattern is not anchored, the
+        at  which  the  current  match  attempt started. However, if the escape
-        callout function may be called several times from the same point in the
+        sequence \K has been encountered, this value is changed to reflect  the
-        pattern for different starting points in the subject.
+        modified  starting  point.  If the pattern is not anchored, the callout
+        function may be called several times from the same point in the pattern
+        for different starting points in the subject.
         The  current_position  field  contains the offset within the subject of
         the current match pointer.
-Line 2211 
 RETURN VALUES
+Line 2578 
 RETURN VALUES
         reserved for use by callout functions; it will never be  used  by  PCRE
         itself.
- Last updated: 28 February 2005
- Copyright (c) 1997-2005 University of Cambridge.
+ AUTHOR
+        Philip Hazel
+        University Computing Service
+        Cambridge CB2 3QH, England.
+ REVISION
+        Last updated: 29 May 2007
+        Copyright (c) 1997-2007 University of Cambridge.
  ------------------------------------------------------------------------------
-Line 2226 
 NAME
+Line 2603 
 NAME
  DIFFERENCES BETWEEN PCRE AND PERL
         This  document describes the differences in the ways that PCRE and Perl
-        handle regular expressions. The differences  described  here  are  with
+        handle regular expressions. The differences described here  are  mainly
-        respect to Perl 5.8.
+        with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain
+        some features that are expected to be in the forthcoming Perl 5.10.
-.  PCRE does not have full UTF-8 support. Details of what it does have
-        are given in the section on UTF-8 support in the main pcre page.
+. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details
+        of  what  it does have are given in the section on UTF-8 support in the
+        main pcre page.
 . PCRE does not allow repeat quantifiers on lookahead assertions. Perl
         permits  them,  but they do not mean what you might think. For example,
-Line 2257 
 DIFFERENCES BETWEEN PCRE AND PERL
+Line 2636 
 DIFFERENCES BETWEEN PCRE AND PERL
 . The Perl escape sequences \p, \P, and \X are supported only if  PCRE
         is  built  with Unicode character property support. The properties that
         can be tested with \p and \P are limited to the general category  prop-
-        erties such as Lu and Nd.
+        erties  such  as  Lu and Nd, script names such as Greek or Han, and the
+        derived properties Any and L&.
 . PCRE does support the \Q...\E escape for quoting substrings. Charac-
-        ters in between are treated as literals.  This  is  slightly  different
+        ters  in  between  are  treated as literals. This is slightly different
-        from  Perl  in  that  $  and  @ are also handled as literals inside the
+        from Perl in that $ and @ are  also  handled  as  literals  inside  the
-        quotes. In Perl, they cause variable interpolation (but of course  PCRE
+        quotes.  In Perl, they cause variable interpolation (but of course PCRE
         does not have variables). Note the following examples:
             Pattern            PCRE matches      Perl matches
-Line 2272 
 DIFFERENCES BETWEEN PCRE AND PERL
+Line 2652 
 DIFFERENCES BETWEEN PCRE AND PERL
             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
-        The  \Q...\E  sequence  is recognized both inside and outside character
+        The \Q...\E sequence is recognized both inside  and  outside  character
         classes.
-. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})
+. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
-        constructions.  However,  there is support for recursive patterns using
+        constructions. However, there is support for recursive  patterns.  This
-        the non-Perl items (?R),  (?number),  and  (?P>name).  Also,  the  PCRE
+        is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE
-        "callout"  feature allows an external function to be called during pat-
+        "callout" feature allows an external function to be called during  pat-
         tern matching. See the pcrecallout documentation for details.
-. There are some differences that are concerned with the  settings  of
+.  Subpatterns  that  are  called  recursively or as "subroutines" are
-        captured  strings  when  part  of  a  pattern is repeated. For example,
+        always treated as atomic groups in  PCRE.  This  is  like  Python,  but
-        matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2
+        unlike Perl.
+.  There are some differences that are concerned with the settings of
+        captured strings when part of  a  pattern  is  repeated.  For  example,
+        matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
         unset, but in PCRE it is set to "b".
 . PCRE provides some extensions to the Perl regular expression facil-
-        ities:
+        ities.   Perl  5.10  will  include new features that are not in earlier
+        versions, some of which (such as named parentheses) have been  in  PCRE
+        for some time. This list is with respect to Perl 5.10:
-        (a) Although lookbehind assertions must  match  fixed  length  strings,
+        (a)  Although  lookbehind  assertions  must match fixed length strings,
         each alternative branch of a lookbehind assertion can match a different
         length of string. Perl requires them all to have the same length.
-        (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the  $
+        (b)  If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
         meta-character matches only at the very end of the string.
         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
-        cial meaning is faulted.
+        cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
+        ignored.  (Perl can be made to issue a warning.)
         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
         fiers is inverted, that is, by default they are not greedy, but if fol-
-Line 2309 
 DIFFERENCES BETWEEN PCRE AND PERL
+Line 2696 
 DIFFERENCES BETWEEN PCRE AND PERL
         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-
         TURE options for pcre_exec() have no Perl equivalents.
-        (g) The (?R), (?number), and (?P>name) constructs allows for  recursive
+        (g) The callout facility is PCRE-specific.
-        pattern  matching  (Perl  can  do  this using the (?p{code}) construct,
-        which PCRE cannot support.)
-        (h) PCRE supports named capturing substrings, using the Python  syntax.
+        (h) The partial matching facility is PCRE-specific.
-        (i)  PCRE  supports  the  possessive quantifier "++" syntax, taken from
+        (i) Patterns compiled by PCRE can be saved and re-used at a later time,
-        Sun's Java package.
+        even on different hosts that have the other endianness.
-        (j) The (R) condition, for testing recursion, is a PCRE extension.
+        (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a
+        different way and is not Perl-compatible.
-        (k) The callout facility is PCRE-specific.
-        (l) The partial matching facility is PCRE-specific.
+ AUTHOR
-        (m) Patterns compiled by PCRE can be saved and re-used at a later time,
+        Philip Hazel
-        even on different hosts that have the other endianness.
+        University Computing Service
+        Cambridge CB2 3QH, England.
-        (n)  The  alternative  matching function (pcre_dfa_exec()) matches in a
-        different way and is not Perl-compatible.
- Last updated: 28 February 2005
+ REVISION
- Copyright (c) 1997-2005 University of Cambridge.
+        Last updated: 13 June 2007
+        Copyright (c) 1997-2007 University of Cambridge.
  ------------------------------------------------------------------------------
-Line 2363 
 PCRE REGULAR EXPRESSION DETAILS
+Line 2749 
 PCRE REGULAR EXPRESSION DETAILS
         ported  by  PCRE when its main matching function, pcre_exec(), is used.
         From  release  6.0,   PCRE   offers   a   second   matching   function,
         pcre_dfa_exec(),  which matches using a different algorithm that is not
-        Perl-compatible. The advantages and disadvantages  of  the  alternative
+        Perl-compatible. Some of the features discussed below are not available
-        function, and how it differs from the normal function, are discussed in
+        when  pcre_dfa_exec()  is used. The advantages and disadvantages of the
-        the pcrematching page.
+        alternative function, and how it differs from the normal function,  are
+        discussed in the pcrematching page.
-        A regular expression is a pattern that is  matched  against  a  subject
-        string  from  left  to right. Most characters stand for themselves in a
-        pattern, and match the corresponding characters in the  subject.  As  a
+ CHARACTERS AND METACHARACTERS
+        A  regular  expression  is  a pattern that is matched against a subject
+        string from left to right. Most characters stand for  themselves  in  a
+        pattern,  and  match  the corresponding characters in the subject. As a
         trivial example, the pattern
           The quick brown fox
         matches a portion of a subject string that is identical to itself. When
-        caseless matching is specified (the PCRE_CASELESS option), letters  are
+        caseless  matching is specified (the PCRE_CASELESS option), letters are
-        matched  independently  of case. In UTF-8 mode, PCRE always understands
+        matched independently of case. In UTF-8 mode, PCRE  always  understands
-        the concept of case for characters whose values are less than  128,  so
+        the  concept  of case for characters whose values are less than 128, so
-        caseless  matching  is always possible. For characters with higher val-
+        caseless matching is always possible. For characters with  higher  val-
-        ues, the concept of case is supported if PCRE is compiled with  Unicode
+        ues,  the concept of case is supported if PCRE is compiled with Unicode
-        property  support,  but  not  otherwise.   If  you want to use caseless
+        property support, but not otherwise.   If  you  want  to  use  caseless
-        matching for characters 128 and above, you must  ensure  that  PCRE  is
+        matching  for  characters  128  and above, you must ensure that PCRE is
         compiled with Unicode property support as well as with UTF-8 support.
-        The  power  of  regular  expressions  comes from the ability to include
+        The power of regular expressions comes  from  the  ability  to  include
-        alternatives and repetitions in the pattern. These are encoded  in  the
+        alternatives  and  repetitions in the pattern. These are encoded in the
         pattern by the use of metacharacters, which do not stand for themselves
         but instead are interpreted in some special way.
-        There are two different sets of metacharacters: those that  are  recog-
+        There  are  two different sets of metacharacters: those that are recog-
-        nized  anywhere in the pattern except within square brackets, and those
+        nized anywhere in the pattern except within square brackets, and  those
-        that are recognized in square brackets. Outside  square  brackets,  the
+        that  are  recognized  within square brackets. Outside square brackets,
-        metacharacters are as follows:
+        the metacharacters are as follows:
           \      general escape character with several uses
           ^      assert start of string (or line, in multiline mode)
-Line 2410 
 PCRE REGULAR EXPRESSION DETAILS
+Line 2800 
 PCRE REGULAR EXPRESSION DETAILS
                  also "possessive quantifier"
           {      start min/max quantifier
-        Part  of  a  pattern  that is in square brackets is called a "character
+        Part of a pattern that is in square brackets  is  called  a  "character
         class". In a character class the only metacharacters are:
           \      general escape character
-Line 2420 
 PCRE REGULAR EXPRESSION DETAILS
+Line 2810 
 PCRE REGULAR EXPRESSION DETAILS
                    syntax)
           ]      terminates the character class
-        The following sections describe the use of each of the  metacharacters.
+        The  following sections describe the use of each of the metacharacters.
  BACKSLASH
         The backslash character has several uses. Firstly, if it is followed by
-        a non-alphanumeric character, it takes away any  special  meaning  that
+        a  non-alphanumeric  character,  it takes away any special meaning that
-        character  may  have.  This  use  of  backslash  as an escape character
+        character may have. This  use  of  backslash  as  an  escape  character
         applies both inside and outside character classes.
-        For example, if you want to match a * character, you write  \*  in  the
+        For  example,  if  you want to match a * character, you write \* in the
-        pattern.   This  escaping  action  applies whether or not the following
+        pattern.  This escaping action applies whether  or  not  the  following
-        character would otherwise be interpreted as a metacharacter, so  it  is
+        character  would  otherwise be interpreted as a metacharacter, so it is
-        always  safe  to  precede  a non-alphanumeric with backslash to specify
+        always safe to precede a non-alphanumeric  with  backslash  to  specify
-        that it stands for itself. In particular, if you want to match a  back-
+        that  it stands for itself. In particular, if you want to match a back-
         slash, you write \\.
-        If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
+        If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in
-        the pattern (other than in a character class) and characters between  a
+        the  pattern (other than in a character class) and characters between a
-        # outside a character class and the next newline character are ignored.
+        # outside a character class and the next newline are ignored. An escap-
-        An escaping backslash can be used to include a whitespace or #  charac-
+        ing  backslash  can  be  used to include a whitespace or # character as
-        ter as part of the pattern.
+        part of the pattern.
-        If  you  want  to remove the special meaning from a sequence of charac-
+        If you want to remove the special meaning from a  sequence  of  charac-
-        ters, you can do so by putting them between \Q and \E. This is  differ-
+        ters,  you can do so by putting them between \Q and \E. This is differ-
-        ent  from  Perl  in  that  $  and  @ are handled as literals in \Q...\E
+        ent from Perl in that $ and  @  are  handled  as  literals  in  \Q...\E
-        sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-
+        sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-
         tion. Note the following examples:
           Pattern            PCRE matches   Perl matches
-Line 2456 
 BACKSLASH
+Line 2846 
 BACKSLASH
           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
-        The  \Q...\E  sequence  is recognized both inside and outside character
+        The \Q...\E sequence is recognized both inside  and  outside  character
         classes.
     Non-printing characters
         A second use of backslash provides a way of encoding non-printing char-
-        acters  in patterns in a visible manner. There is no restriction on the
+        acters in patterns in a visible manner. There is no restriction on  the
-        appearance of non-printing characters, apart from the binary zero  that
+        appearance  of non-printing characters, apart from the binary zero that
-        terminates  a  pattern,  but  when  a pattern is being prepared by text
+        terminates a pattern, but when a pattern  is  being  prepared  by  text
-        editing, it is usually easier  to  use  one  of  the  following  escape
+        editing,  it  is  usually  easier  to  use  one of the following escape
         sequences than the binary character it represents:
           \a        alarm, that is, the BEL character (hex 07)
-Line 2477 
 BACKSLASH
+Line 2867 
 BACKSLASH
           \t        tab (hex 09)
           \ddd      character with octal code ddd, or backreference
           \xhh      character with hex code hh
-          \x{hhh..} character with hex code hhh... (UTF-8 mode only)
+          \x{hhh..} character with hex code hhh..
-        The  precise  effect of \cx is as follows: if x is a lower case letter,
+        The precise effect of \cx is as follows: if x is a lower  case  letter,
-        it is converted to upper case. Then bit 6 of the character (hex 40)  is
+        it  is converted to upper case. Then bit 6 of the character (hex 40) is
-        inverted.   Thus  \cz becomes hex 1A, but \c{ becomes hex 3B, while \c;
+        inverted.  Thus \cz becomes hex 1A, but \c{ becomes hex 3B,  while  \c;
         becomes hex 7B.
-        After \x, from zero to two hexadecimal digits are read (letters can  be
+        After  \x, from zero to two hexadecimal digits are read (letters can be
-        in  upper or lower case). In UTF-8 mode, any number of hexadecimal dig-
+        in upper or lower case). Any number of hexadecimal  digits  may  appear
-        its may appear between \x{ and }, but the value of the  character  code
+        between  \x{  and  },  but the value of the character code must be less
-        must  be  less  than  2**31  (that is, the maximum hexadecimal value is
+        than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode (that is,
-FFFFFFF). If characters other than hexadecimal digits  appear  between
+        the  maximum  hexadecimal  value is 7FFFFFFF). If characters other than
-        \x{  and }, or if there is no terminating }, this form of escape is not
+        hexadecimal digits appear between \x{ and }, or if there is  no  termi-
-        recognized. Instead, the initial \x will  be  interpreted  as  a  basic
+        nating  }, this form of escape is not recognized.  Instead, the initial
-        hexadecimal  escape, with no following digits, giving a character whose
+        \x will be interpreted as a basic hexadecimal escape, with no following
-        value is zero.
+        digits, giving a character whose value is zero.
         Characters whose value is less than 256 can be defined by either of the
-        two  syntaxes for \x when PCRE is in UTF-8 mode. There is no difference
+        two syntaxes for \x. There is no difference in the way  they  are  han-
-        in the way they are handled. For example, \xdc is exactly the  same  as
+        dled. For example, \xdc is exactly the same as \x{dc}.
-        \x{dc}.
+        After  \0  up  to two further octal digits are read. If there are fewer
-        After  \0  up  to  two further octal digits are read. In both cases, if
+        than two digits, just  those  that  are  present  are  used.  Thus  the
-        there are fewer than two digits, just those that are present are  used.
+        sequence \0\x\07 specifies two binary zeros followed by a BEL character
-        Thus  the sequence \0\x\07 specifies two binary zeros followed by a BEL
+        (code value 7). Make sure you supply two digits after the initial  zero
-        character (code value 7). Make sure you supply  two  digits  after  the
+        if the pattern character that follows is itself an octal digit.
-        initial  zero  if the pattern character that follows is itself an octal
-        digit.
         The handling of a backslash followed by a digit other than 0 is compli-
         cated.  Outside a character class, PCRE reads it and any following dig-
-        its as a decimal number. If the number is less than  10,  or  if  there
+        its  as  a  decimal  number. If the number is less than 10, or if there
         have been at least that many previous capturing left parentheses in the
-        expression, the entire  sequence  is  taken  as  a  back  reference.  A
+        expression,  the  entire  sequence  is  taken  as  a  back reference. A
-        description  of how this works is given later, following the discussion
+        description of how this works is given later, following the  discussion
         of parenthesized subpatterns.
-        Inside a character class, or if the decimal number is  greater  than  9
+        Inside  a  character  class, or if the decimal number is greater than 9
-        and  there have not been that many capturing subpatterns, PCRE re-reads
+        and there have not been that many capturing subpatterns, PCRE  re-reads
-        up to three octal digits following the backslash, and generates a  sin-
+        up to three octal digits following the backslash, and uses them to gen-
-        gle byte from the least significant 8 bits of the value. Any subsequent
+        erate a data character. Any subsequent digits stand for themselves.  In
-        digits stand for themselves.  For example:
+        non-UTF-8  mode,  the  value  of a character specified in octal must be
+        less than \400. In UTF-8 mode, values up to  \777  are  permitted.  For
+        example:
           \040   is another way of writing a space
           \40    is the same, provided there are fewer than 40
-Line 2535 
 BACKSLASH
+Line 2925 
 BACKSLASH
           \81    is either a back reference, or a binary zero
                     followed by the two characters "8" and "1"
-        Note that octal values of 100 or greater must not be  introduced  by  a
+        Note  that  octal  values of 100 or greater must not be introduced by a
         leading zero, because no more than three octal digits are ever read.
-        All  the  sequences  that  define a single byte value or a single UTF-8
+        All the sequences that define a single character value can be used both
-        character (in UTF-8 mode) can be used both inside and outside character
+        inside  and  outside character classes. In addition, inside a character
-        classes.  In  addition,  inside  a  character class, the sequence \b is
+        class, the sequence \b is interpreted as the backspace  character  (hex
-        interpreted as the backspace character (hex 08), and the sequence \X is
+),  and the sequences \R and \X are interpreted as the characters "R"
-        interpreted  as  the  character  "X".  Outside a character class, these
+        and "X", respectively. Outside a character class, these sequences  have
-        sequences have different meanings (see below).
+        different meanings (see below).
+    Absolute and relative back references
+        The  sequence  \g followed by a positive or negative number, optionally
+        enclosed in braces, is an absolute or relative back reference. A  named
+        back  reference can be coded as \g{name}. Back references are discussed
+        later, following the discussion of parenthesized subpatterns.
     Generic character types
-        The third use of backslash is for specifying generic  character  types.
+        Another use of backslash is for specifying generic character types. The
-        The following are always recognized:
+        following are always recognized:
           \d     any decimal digit
           \D     any character that is not a decimal digit
+          \h     any horizontal whitespace character
+          \H     any character that is not a horizontal whitespace character
           \s     any whitespace character
           \S     any character that is not a whitespace character
+          \v     any vertical whitespace character
+          \V     any character that is not a vertical whitespace character
           \w     any "word" character
           \W     any "non-word" character
-Line 2568 
 BACKSLASH
+Line 2969 
 BACKSLASH
         For compatibility with Perl, \s does not match the VT  character  (code
 ).   This makes it different from the the POSIX "space" class. The \s
-        characters are HT (9), LF (10), FF (12), CR (13), and space (32).
+        characters are HT (9), LF (10), FF (12), CR (13), and  space  (32).  If
+        "use locale;" is included in a Perl script, \s may match the VT charac-
+        ter. In PCRE, it never does.
+        In UTF-8 mode, characters with values greater than 128 never match  \d,
+        \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
+        code character property support is available.  These  sequences  retain
+        their original meanings from before UTF-8 support was available, mainly
+        for efficiency reasons.
+        The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
+        the  other  sequences, these do match certain high-valued codepoints in
+        UTF-8 mode.  The horizontal space characters are:
+          U+0009     Horizontal tab
+          U+0020     Space
+          U+00A0     Non-break space
+          U+1680     Ogham space mark
+          U+180E     Mongolian vowel separator
+          U+2000     En quad
+          U+2001     Em quad
+          U+2002     En space
+          U+2003     Em space
+          U+2004     Three-per-em space
+          U+2005     Four-per-em space
+          U+2006     Six-per-em space
+          U+2007     Figure space
+          U+2008     Punctuation space
+          U+2009     Thin space
+          U+200A     Hair space
+          U+202F     Narrow no-break space
+          U+205F     Medium mathematical space
+          U+3000     Ideographic space
+        The vertical space characters are:
+          U+000A     Linefeed
+          U+000B     Vertical tab
+          U+000C     Formfeed
+          U+000D     Carriage return
+          U+0085     Next line
+          U+2028     Line separator
+          U+2029     Paragraph separator
         A "word" character is an underscore or any character less than 256 that
         is  a  letter  or  digit.  The definition of letters and digits is con-
         trolled by PCRE's low-valued character tables, and may vary if  locale-
         specific  matching is taking place (see "Locale support" in the pcreapi
-        page). For example, in the  "fr_FR"  (French)  locale,  some  character
+        page). For example, in a French locale such  as  "fr_FR"  in  Unix-like
-        codes  greater  than  128  are used for accented letters, and these are
+        systems,  or "french" in Windows, some character codes greater than 128
-        matched by \w.
+        are used for accented letters, and these are matched by \w. The use  of
+        locales with Unicode is discouraged.
+    Newline sequences
+        Outside  a  character class, the escape sequence \R matches any Unicode
+        newline sequence. This is a Perl 5.10 feature. In non-UTF-8 mode \R  is
+        equivalent to the following:
+          (?>\r\n|\n|\x0b|\f|\r|\x85)
+        This  is  an  example  of an "atomic group", details of which are given
+        below.  This particular group matches either the two-character sequence
+        CR  followed  by  LF,  or  one  of  the single characters LF (linefeed,
+        U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
+        return, U+000D), or NEL (next line, U+0085). The two-character sequence
+        is treated as a single unit that cannot be split.
+        In UTF-8 mode, two additional characters whose codepoints  are  greater
+        than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
+        rator, U+2029).  Unicode character property support is not  needed  for
+        these characters to be recognized.
-        In UTF-8 mode, characters with values greater than 128 never match  \d,
+        Inside a character class, \R matches the letter "R".
-        \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
-        code character property support is available.
     Unicode character properties
         When PCRE is built with Unicode character property support, three addi-
-        tional  escape sequences to match generic character types are available
+        tional escape sequences that match characters with specific  properties
-        when UTF-8 mode is selected. They are:
+        are  available.   When not in UTF-8 mode, these sequences are of course
+        limited to testing characters whose codepoints are less than  256,  but
-         \p{xx}   a character with the xx property
+        they do work in this mode.  The extra escape sequences are:
-         \P{xx}   a character without the xx property
-         \X       an extended Unicode sequence
+          \p{xx}   a character with the xx property
+          \P{xx}   a character without the xx property
-        The property names represented by xx above are limited to  the  Unicode
+          \X       an extended Unicode sequence
-        general  category properties. Each character has exactly one such prop-
-        erty, specified by a two-letter abbreviation.  For  compatibility  with
+        The  property  names represented by xx above are limited to the Unicode
-        Perl,  negation  can be specified by including a circumflex between the
+        script names, the general category properties, and "Any", which matches
-        opening brace and the property name. For example, \p{^Lu} is  the  same
+        any character (including newline). Other properties such as "InMusical-
-        as \P{Lu}.
+        Symbols" are not currently supported by PCRE. Note  that  \P{Any}  does
+        not match any characters, so always causes a match failure.
-        If  only  one  letter  is  specified with \p or \P, it includes all the
-        properties that start with that letter. In this case, in the absence of
+        Sets of Unicode characters are defined as belonging to certain scripts.
-        negation, the curly brackets in the escape sequence are optional; these
+        A character from one of these sets can be matched using a script  name.
-        two examples have the same effect:
+        For example:
+          \p{Greek}
+          \P{Han}
+        Those  that are not part of an identified script are lumped together as
+        "Common". The current list of scripts is:
+        Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
+        Buhid,   Canadian_Aboriginal,   Cherokee,  Common,  Coptic,  Cuneiform,
+        Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
+        Gothic,  Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
+        gana, Inherited, Kannada,  Katakana,  Kharoshthi,  Khmer,  Lao,  Latin,
+        Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
+        Ogham, Old_Italic, Old_Persian, Oriya, Osmanya,  Phags_Pa,  Phoenician,
+        Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
+        Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
+        Each character has exactly one general category property, specified  by
+        a two-letter abbreviation. For compatibility with Perl, negation can be
+        specified by including a circumflex between the opening brace  and  the
+        property name. For example, \p{^Lu} is the same as \P{Lu}.
+        If only one letter is specified with \p or \P, it includes all the gen-
+        eral category properties that start with that letter. In this case,  in
+        the  absence of negation, the curly brackets in the escape sequence are
+        optional; these two examples have the same effect:
           \p{L}
           \pL
-        The following property codes are supported:
+        The following general category property codes are supported:
           C     Other
           Cc    Control
-Line 2653 
 BACKSLASH
+Line 3141 
 BACKSLASH
           Zp    Paragraph separator
           Zs    Space separator
-        Extended properties such as "Greek" or "InMusicalSymbols" are not  sup-
+        The special property L& is also supported: it matches a character  that
-        ported by PCRE.
+        has  the  Lu,  Ll, or Lt property, in other words, a letter that is not
+        classified as a modifier or "other".
+        The long synonyms for these properties  that  Perl  supports  (such  as
+        \p{Letter})  are  not  supported by PCRE, nor is it permitted to prefix
+        any of these properties with "Is".
+        No character that is in the Unicode table has the Cn (unassigned) prop-
+        erty.  Instead, this property is assumed for any code point that is not
+        in the Unicode table.
-        Specifying  caseless  matching  does not affect these escape sequences.
+        Specifying caseless matching does not affect  these  escape  sequences.
         For example, \p{Lu} always matches only upper case letters.
-        The \X escape matches any number of Unicode  characters  that  form  an
+        The  \X  escape  matches  any number of Unicode characters that form an
         extended Unicode sequence. \X is equivalent to
           (?>\PM\pM*)
-        That  is,  it matches a character without the "mark" property, followed
+        That is, it matches a character without the "mark"  property,  followed
-        by zero or more characters with the "mark"  property,  and  treats  the
+        by  zero  or  more  characters with the "mark" property, and treats the
-        sequence  as  an  atomic group (see below).  Characters with the "mark"
+        sequence as an atomic group (see below).  Characters  with  the  "mark"
-        property are typically accents that affect the preceding character.
+        property  are  typically  accents  that affect the preceding character.
+        None of them have codepoints less than 256, so  in  non-UTF-8  mode  \X
+        matches any one character.
-        Matching characters by Unicode property is not fast, because  PCRE  has
+        Matching  characters  by Unicode property is not fast, because PCRE has
-        to  search  a  structure  that  contains data for over fifteen thousand
+        to search a structure that contains  data  for  over  fifteen  thousand
         characters. That is why the traditional escape sequences such as \d and
         \w do not use Unicode properties in PCRE.
+    Resetting the match start
+        The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
+        ously  matched  characters  not  to  be  included  in the final matched
+        sequence. For example, the pattern:
+          foo\Kbar
+        matches "foobar", but reports that it has matched "bar".  This  feature
+        is  similar  to  a lookbehind assertion (described below).  However, in
+        this case, the part of the subject before the real match does not  have
+        to  be of fixed length, as lookbehind assertions do. The use of \K does
+        not interfere with the setting of captured  substrings.   For  example,
+        when the pattern
+          (foo)\Kbar
+        matches "foobar", the first substring is still set to "foo".
     Simple assertions
-        The fourth use of backslash is for certain simple assertions. An asser-
+        The  final use of backslash is for certain simple assertions. An asser-
         tion specifies a condition that has to be met at a particular point  in
         a  match, without consuming any characters from the subject string. The
         use of subpatterns for more complicated assertions is described  below.
-Line 2684 
 BACKSLASH
+Line 3202 
 BACKSLASH
           \b     matches at a word boundary
           \B     matches when not at a word boundary
-          \A     matches at start of subject
+          \A     matches at the start of the subject
-          \Z     matches at end of subject or before newline at end
+          \Z     matches at the end of the subject
-          \z     matches at end of subject
+                  also matches before a newline at the end of the subject
-          \G     matches at first matching position in subject
+          \z     matches only at the end of the subject
+          \G     matches at the first matching position in the subject
         These  assertions may not appear in character classes (but note that \b
         has a different meaning, namely the backspace character, inside a char-
-Line 2707 
 BACKSLASH
+Line 3226 
 BACKSLASH
         However, if the startoffset argument of pcre_exec() is non-zero,  indi-
         cating that matching is to start at a point other than the beginning of
         the subject, \A can never match. The difference between \Z  and  \z  is
-        that  \Z  matches  before  a  newline that is the last character of the
+        that \Z matches before a newline at the end of the string as well as at
-        string as well as at the end of the string, whereas \z matches only  at
+        the very end, whereas \z matches only at the end.
-        the end.
+        The \G assertion is true only when the current matching position is  at
-        The  \G assertion is true only when the current matching position is at
+        the  start point of the match, as specified by the startoffset argument
-        the start point of the match, as specified by the startoffset  argument
+        of pcre_exec(). It differs from \A when the  value  of  startoffset  is
-        of  pcre_exec().  It  differs  from \A when the value of startoffset is
+        non-zero.  By calling pcre_exec() multiple times with appropriate argu-
-        non-zero. By calling pcre_exec() multiple times with appropriate  argu-
         ments, you can mimic Perl's /g option, and it is in this kind of imple-
         mentation where \G can be useful.
-        Note, however, that PCRE's interpretation of \G, as the  start  of  the
+        Note,  however,  that  PCRE's interpretation of \G, as the start of the
         current match, is subtly different from Perl's, which defines it as the
-        end of the previous match. In Perl, these can  be  different  when  the
+        end  of  the  previous  match. In Perl, these can be different when the
-        previously  matched  string was empty. Because PCRE does just one match
+        previously matched string was empty. Because PCRE does just  one  match
         at a time, it cannot reproduce this behaviour.
-        If all the alternatives of a pattern begin with \G, the  expression  is
+        If  all  the alternatives of a pattern begin with \G, the expression is
         anchored to the starting match position, and the "anchored" flag is set
         in the compiled regular expression.
-Line 2732 
 BACKSLASH
+Line 3250 
 BACKSLASH
  CIRCUMFLEX AND DOLLAR
         Outside a character class, in the default matching mode, the circumflex
-        character  is  an  assertion  that is true only if the current matching
+        character is an assertion that is true only  if  the  current  matching
-        point is at the start of the subject string. If the  startoffset  argu-
+        point  is  at the start of the subject string. If the startoffset argu-
-        ment  of  pcre_exec()  is  non-zero,  circumflex can never match if the
+        ment of pcre_exec() is non-zero, circumflex  can  never  match  if  the
-        PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex
+        PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex
         has an entirely different meaning (see below).
-        Circumflex  need  not be the first character of the pattern if a number
+        Circumflex need not be the first character of the pattern if  a  number
-        of alternatives are involved, but it should be the first thing in  each
+        of  alternatives are involved, but it should be the first thing in each
-        alternative  in  which  it appears if the pattern is ever to match that
+        alternative in which it appears if the pattern is ever  to  match  that
-        branch. If all possible alternatives start with a circumflex, that  is,
+        branch.  If all possible alternatives start with a circumflex, that is,
-        if  the  pattern  is constrained to match only at the start of the sub-
+        if the pattern is constrained to match only at the start  of  the  sub-
-        ject, it is said to be an "anchored" pattern.  (There  are  also  other
+        ject,  it  is  said  to be an "anchored" pattern. (There are also other
         constructs that can cause a pattern to be anchored.)
-        A  dollar  character  is  an assertion that is true only if the current
+        A dollar character is an assertion that is true  only  if  the  current
-        matching point is at the end of  the  subject  string,  or  immediately
+        matching  point  is  at  the  end of the subject string, or immediately
-        before a newline character that is the last character in the string (by
+        before a newline at the end of the string (by default). Dollar need not
-        default). Dollar need not be the last character of  the  pattern  if  a
+        be  the  last  character of the pattern if a number of alternatives are
-        number  of alternatives are involved, but it should be the last item in
+        involved, but it should be the last item in  any  branch  in  which  it
-        any branch in which it appears.  Dollar has no  special  meaning  in  a
+        appears. Dollar has no special meaning in a character class.
-        character class.
         The  meaning  of  dollar  can be changed so that it matches only at the
         very end of the string, by setting the  PCRE_DOLLAR_ENDONLY  option  at
         compile time. This does not affect the \Z assertion.
         The meanings of the circumflex and dollar characters are changed if the
-        PCRE_MULTILINE option is set. When this is the case, they match immedi-
+        PCRE_MULTILINE option is set. When  this  is  the  case,  a  circumflex
-        ately  after  and  immediately  before  an  internal newline character,
+        matches  immediately after internal newlines as well as at the start of
-        respectively, in addition to matching at the start and end of the  sub-
+        the subject string. It does not match after a  newline  that  ends  the
-        ject  string.  For  example,  the  pattern  /^abc$/ matches the subject
+        string.  A dollar matches before any newlines in the string, as well as
-        string "def\nabc" (where \n represents a newline character)  in  multi-
+        at the very end, when PCRE_MULTILINE is set. When newline is  specified
-        line mode, but not otherwise.  Consequently, patterns that are anchored
+        as  the  two-character  sequence CRLF, isolated CR and LF characters do
-        in single line mode because all branches start with ^ are not  anchored
+        not indicate newlines.
-        in  multiline  mode,  and  a  match for circumflex is possible when the
-        startoffset  argument  of  pcre_exec()  is  non-zero.   The   PCRE_DOL-
+        For example, the pattern /^abc$/ matches the subject string  "def\nabc"
-        LAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
+        (where  \n  represents a newline) in multiline mode, but not otherwise.
+        Consequently, patterns that are anchored in single  line  mode  because
-        Note  that  the sequences \A, \Z, and \z can be used to match the start
+        all  branches  start  with  ^ are not anchored in multiline mode, and a
-        and end of the subject in both modes, and if all branches of a  pattern
+        match for circumflex is  possible  when  the  startoffset  argument  of
-        start  with  \A it is always anchored, whether PCRE_MULTILINE is set or
+        pcre_exec()  is  non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
-        not.
+        PCRE_MULTILINE is set.
+        Note that the sequences \A, \Z, and \z can be used to match  the  start
+        and  end of the subject in both modes, and if all branches of a pattern
+        start with \A it is always anchored, whether or not  PCRE_MULTILINE  is
+        set.
  FULL STOP (PERIOD, DOT)
         Outside a character class, a dot in the pattern matches any one charac-
-        ter  in  the  subject,  including a non-printing character, but not (by
+        ter in the subject string except (by default) a character  that  signi-
-        default) newline.  In UTF-8 mode, a dot matches  any  UTF-8  character,
+        fies  the  end  of  a line. In UTF-8 mode, the matched character may be
-        which might be more than one byte long, except (by default) newline. If
+        more than one byte long.
-        the PCRE_DOTALL option is set, dots match newlines as  well.  The  han-
-        dling  of dot is entirely independent of the handling of circumflex and
+        When a line ending is defined as a single character, dot never  matches
-        dollar, the only relationship being  that  they  both  involve  newline
+        that  character; when the two-character sequence CRLF is used, dot does
-        characters. Dot has no special meaning in a character class.
+        not match CR if it is immediately followed  by  LF,  but  otherwise  it
+        matches  all characters (including isolated CRs and LFs). When any Uni-
+        code line endings are being recognized, dot does not match CR or LF  or
+        any of the other line ending characters.
+        The  behaviour  of  dot  with regard to newlines can be changed. If the
+        PCRE_DOTALL option is set, a dot matches  any  one  character,  without
+        exception. If the two-character sequence CRLF is present in the subject
+        string, it takes two dots to match it.
+        The handling of dot is entirely independent of the handling of  circum-
+        flex  and  dollar,  the  only relationship being that they both involve
+        newlines. Dot has no special meaning in a character class.
  MATCHING A SINGLE BYTE
         Outside a character class, the escape sequence \C matches any one byte,
-        both in and out of UTF-8 mode. Unlike a dot, it can  match  a  newline.
+        both  in  and  out  of  UTF-8 mode. Unlike a dot, it always matches any
-        The  feature  is provided in Perl in order to match individual bytes in
+        line-ending characters. The feature is provided in  Perl  in  order  to
-        UTF-8 mode. Because it  breaks  up  UTF-8  characters  into  individual
+        match  individual bytes in UTF-8 mode. Because it breaks up UTF-8 char-
-        bytes,  what remains in the string may be a malformed UTF-8 string. For
+        acters into individual bytes, what remains in the string may be a  mal-
-        this reason, the \C escape sequence is best avoided.
+        formed  UTF-8  string.  For this reason, the \C escape sequence is best
+        avoided.
         PCRE does not allow \C to appear in  lookbehind  assertions  (described
         below),  because  in UTF-8 mode this would make it impossible to calcu-
-Line 2842 
 SQUARE BRACKETS AND CHARACTER CLASSES
+Line 3377 
 SQUARE BRACKETS AND CHARACTER CLASSES
         PCRE  is  compiled  with Unicode property support as well as with UTF-8
         support.
-        The newline character is never treated in any special way in  character
+        Characters that might indicate line breaks are  never  treated  in  any
-        classes,  whatever  the  setting  of  the PCRE_DOTALL or PCRE_MULTILINE
+        special  way  when  matching  character  classes,  whatever line-ending
-        options is. A class such as [^a] will always match a newline.
+        sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and
+        PCRE_MULTILINE options is used. A class such as [^a] always matches one
+        of these characters.
         The minus (hyphen) character can be used to specify a range of  charac-
         ters  in  a  character  class.  For  example,  [d-m] matches any letter
-Line 2870 
 SQUARE BRACKETS AND CHARACTER CLASSES
+Line 3407 
 SQUARE BRACKETS AND CHARACTER CLASSES
         If a range that includes letters is used when caseless matching is set,
         it matches the letters in either case. For example, [W-c] is equivalent
         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if
-        character tables for the "fr_FR" locale are in use, [\xc8-\xcb] matches
+        character tables for a French locale are in  use,  [\xc8-\xcb]  matches
         accented  E  characters in both cases. In UTF-8 mode, PCRE supports the
         concept of case for characters with values greater than 128  only  when
         it is compiled with Unicode property support.
-Line 2945 
 VERTICAL BAR
+Line 3482 
 VERTICAL BAR
         matches  either "gilbert" or "sullivan". Any number of alternatives may
         appear, and an empty  alternative  is  permitted  (matching  the  empty
-        string).   The  matching  process  tries each alternative in turn, from
+        string). The matching process tries each alternative in turn, from left
-        left to right, and the first one that succeeds is used. If the alterna-
+        to right, and the first one that succeeds is used. If the  alternatives
-        tives  are within a subpattern (defined below), "succeeds" means match-
+        are  within a subpattern (defined below), "succeeds" means matching the
-        ing the rest of the main pattern as well as the alternative in the sub-
+        rest of the main pattern as well as the alternative in the  subpattern.
-        pattern.
  INTERNAL OPTION SETTING
-Line 2977 
 INTERNAL OPTION SETTING
+Line 3513 
 INTERNAL OPTION SETTING
         PCRE extracts it into the global options (and it will therefore show up
         in data extracted by the pcre_fullinfo() function).
-        An option change within a subpattern affects only that part of the cur-
+        An  option  change  within a subpattern (see below for a description of
-        rent pattern that follows it, so
+        subpatterns) affects only that part of the current pattern that follows
+        it, so
           (a(?i)b)c
         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
-        used).   By  this means, options can be made to have different settings
+        used).  By this means, options can be made to have  different  settings
-        in different parts of the pattern. Any changes made in one  alternative
+        in  different parts of the pattern. Any changes made in one alternative
-        do  carry  on  into subsequent branches within the same subpattern. For
+        do carry on into subsequent branches within the  same  subpattern.  For
         example,
           (a(?i)b|c)
-        matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the
+        matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the
-        first  branch  is  abandoned before the option setting. This is because
+        first branch is abandoned before the option setting.  This  is  because
-        the effects of option settings happen at compile time. There  would  be
+        the  effects  of option settings happen at compile time. There would be
         some very weird behaviour otherwise.
-        The  PCRE-specific  options PCRE_UNGREEDY and PCRE_EXTRA can be changed
+        The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA
-        in the same way as the Perl-compatible options by using the  characters
+        can  be changed in the same way as the Perl-compatible options by using
-        U  and X respectively. The (?X) flag setting is special in that it must
+        the characters J, U and X respectively.
-        always occur earlier in the pattern than any of the additional features
-        it  turns on, even when it is at top level. It is best to put it at the
-        start.
  SUBPATTERNS
-Line 3013 
 SUBPATTERNS
+Line 3547 
 SUBPATTERNS
           cat(aract|erpillar|)
         matches  one  of the words "cat", "cataract", or "caterpillar". Without
-        the parentheses, it would match "cataract",  "erpillar"  or  the  empty
+        the parentheses, it would match  "cataract",  "erpillar"  or  an  empty
         string.
 .  It  sets  up  the  subpattern as a capturing subpattern. This means
-Line 3042 
 SUBPATTERNS
+Line 3576 
 SUBPATTERNS
           the ((?:red|white) (king|queen))
         the captured substrings are "white queen" and "queen", and are numbered
- and 2. The maximum number of capturing subpatterns is 65535, and the
+and 2. The maximum number of capturing subpatterns is 65535.
-        maximum depth of nesting of all subpatterns, both  capturing  and  non-
-        capturing, is 200.
         As  a  convenient shorthand, if any option settings are required at the
         start of a non-capturing subpattern,  the  option  letters  may  appear
-Line 3060 
 SUBPATTERNS
+Line 3592 
 SUBPATTERNS
         "Saturday".
+ DUPLICATE SUBPATTERN NUMBERS
+        Perl 5.10 introduced a feature whereby each alternative in a subpattern
+        uses the same numbers for its capturing parentheses. Such a  subpattern
+        starts  with (?| and is itself a non-capturing subpattern. For example,
+        consider this pattern:
+          (?|(Sat)ur|(Sun))day
+        Because the two alternatives are inside a (?| group, both sets of  cap-
+        turing  parentheses  are  numbered one. Thus, when the pattern matches,
+        you can look at captured substring number  one,  whichever  alternative
+        matched.  This  construct  is useful when you want to capture part, but
+        not all, of one of a number of alternatives. Inside a (?| group, paren-
+        theses  are  numbered as usual, but the number is reset at the start of
+        each branch. The numbers of any capturing buffers that follow the  sub-
+        pattern  start after the highest number used in any branch. The follow-
+        ing example is taken from the Perl documentation.  The  numbers  under-
+        neath show in which buffer the captured content will be stored.
+          # before  ---------------branch-reset----------- after
+          / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
+          # 1            2         2  3        2     3     4
+        A  backreference  or  a  recursive call to a numbered subpattern always
+        refers to the first one in the pattern with the given number.
+        An alternative approach to using this "branch reset" feature is to  use
+        duplicate named subpatterns, as described in the next section.
  NAMED SUBPATTERNS
         Identifying  capturing  parentheses  by number is simple, but it can be
         very hard to keep track of the numbers in complicated  regular  expres-
         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
         change. To help with this difficulty, PCRE supports the naming of  sub-
-        patterns,  something  that  Perl  does  not  provide. The Python syntax
+        patterns. This feature was not added to Perl until release 5.10. Python
-        (?P<name>...) is used. Names consist  of  alphanumeric  characters  and
+        had the feature earlier, and PCRE introduced it at release  4.0,  using
-        underscores, and must be unique within a pattern.
+        the  Python syntax. PCRE now supports both the Perl and the Python syn-
+        tax.
+        In PCRE, a subpattern can be named in one of three  ways:  (?<name>...)
+        or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References
+        to capturing parentheses from other parts of the pattern, such as back-
+        references,  recursion,  and conditions, can be made by name as well as
+        by number.
+        Names consist of up to  32  alphanumeric  characters  and  underscores.
         Named  capturing  parentheses  are  still  allocated numbers as well as
-        names. The PCRE API provides function calls for extracting the name-to-
+        names, exactly as if the names were not present. The PCRE API  provides
-        number  translation table from a compiled pattern. There is also a con-
+        function calls for extracting the name-to-number translation table from
-        venience function for extracting a captured substring by name. For fur-
+        a compiled pattern. There is also a convenience function for extracting
-        ther details see the pcreapi documentation.
+        a captured substring by name.
+        By  default, a name must be unique within a pattern, but it is possible
+        to relax this constraint by setting the PCRE_DUPNAMES option at compile
+        time.  This  can  be useful for patterns where only one instance of the
+        named parentheses can match. Suppose you want to match the  name  of  a
+        weekday,  either as a 3-letter abbreviation or as the full name, and in
+        both cases you want to extract the abbreviation. This pattern (ignoring
+        the line breaks) does the job:
+          (?<DN>Mon|Fri|Sun)(?:day)?|
+          (?<DN>Tue)(?:sday)?|
+          (?<DN>Wed)(?:nesday)?|
+          (?<DN>Thu)(?:rsday)?|
+          (?<DN>Sat)(?:urday)?
+        There  are  five capturing substrings, but only one is ever set after a
+        match.  (An alternative way of solving this problem is to use a "branch
+        reset" subpattern, as described in the previous section.)
+        The  convenience  function  for extracting the data by name returns the
+        substring for the first (and in this example, the only)  subpattern  of
+        that  name  that  matched.  This saves searching to find which numbered
+        subpattern it was. If you make a reference to a non-unique  named  sub-
+        pattern  from elsewhere in the pattern, the one that corresponds to the
+        lowest number is used. For further details of the interfaces  for  han-
+        dling named subpatterns, see the pcreapi documentation.
  REPETITION
-Line 3083 
 REPETITION
+Line 3680 
 REPETITION
         following items:
           a literal data character
-          the . metacharacter
+          the dot metacharacter
           the \C escape sequence
           the \X escape sequence (in UTF-8 mode with Unicode properties)
+          the \R escape sequence
           an escape such as \d that matches a single character
           a character class
           a back reference (see next section)
-Line 3125 
 REPETITION
+Line 3723 
 REPETITION
         The quantifier {0} is permitted, causing the expression to behave as if
         the previous item and the quantifier were not present.
-        For  convenience  (and  historical compatibility) the three most common
+        For  convenience, the three most common quantifiers have single-charac-
-        quantifiers have single-character abbreviations:
+        ter abbreviations:
           *    is equivalent to {0,}
           +    is equivalent to {1,}
-Line 3178 
 REPETITION
+Line 3776 
 REPETITION
         which matches one digit by preference, but can match two if that is the
         only way the rest of the pattern matches.
-        If the PCRE_UNGREEDY option is set (an option which is not available in
+        If the PCRE_UNGREEDY option is set (an option that is not available  in
         Perl),  the  quantifiers are not greedy by default, but individual ones
         can be made greedy by following them with a  question  mark.  In  other
         words, it inverts the default behaviour.
-Line 3189 
 REPETITION
+Line 3787 
 REPETITION
         minimum or maximum.
         If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-
-        alent  to Perl's /s) is set, thus allowing the . to match newlines, the
+        alent  to  Perl's  /s) is set, thus allowing the dot to match newlines,
-        pattern is implicitly anchored, because whatever follows will be  tried
+        the pattern is implicitly anchored, because whatever  follows  will  be
-        against  every character position in the subject string, so there is no
+        tried  against every character position in the subject string, so there
-        point in retrying the overall match at any position  after  the  first.
+        is no point in retrying the overall match at  any  position  after  the
-        PCRE normally treats such a pattern as though it were preceded by \A.
+        first.  PCRE  normally treats such a pattern as though it were preceded
+        by \A.
-        In  cases  where  it  is known that the subject string contains no new-
+        In cases where it is known that the subject  string  contains  no  new-
-        lines, it is worth setting PCRE_DOTALL in order to  obtain  this  opti-
+        lines,  it  is  worth setting PCRE_DOTALL in order to obtain this opti-
         mization, or alternatively using ^ to indicate anchoring explicitly.
-        However,  there is one situation where the optimization cannot be used.
+        However, there is one situation where the optimization cannot be  used.
-        When .*  is inside capturing parentheses that  are  the  subject  of  a
+        When  .*   is  inside  capturing  parentheses that are the subject of a
-        backreference  elsewhere in the pattern, a match at the start may fail,
+        backreference elsewhere in the pattern, a match at the start  may  fail
-        and a later one succeed. Consider, for example:
+        where a later one succeeds. Consider, for example:
           (.*)abc\1
-        If the subject is "xyz123abc123" the match point is the fourth  charac-
+        If  the subject is "xyz123abc123" the match point is the fourth charac-
         ter. For this reason, such a pattern is not implicitly anchored.
         When a capturing subpattern is repeated, the value captured is the sub-
-Line 3215 
 REPETITION
+Line 3814 
 REPETITION
           (tweedle[dume]{3}\s*)+
         has matched "tweedledum tweedledee" the value of the captured substring
-        is  "tweedledee".  However,  if there are nested capturing subpatterns,
+        is "tweedledee". However, if there are  nested  capturing  subpatterns,
-        the corresponding captured values may have been set in previous  itera-
+        the  corresponding captured values may have been set in previous itera-
         tions. For example, after
           /(a|(b))+/
-Line 3226 
 REPETITION
+Line 3825 
 REPETITION
  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
-        With both maximizing and minimizing repetition, failure of what follows
+        With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")
-        normally causes the repeated item to be re-evaluated to see if  a  dif-
+        repetition,  failure  of what follows normally causes the repeated item
-        ferent number of repeats allows the rest of the pattern to match. Some-
+        to be re-evaluated to see if a different number of repeats  allows  the
-        times it is useful to prevent this, either to change the nature of  the
+        rest  of  the pattern to match. Sometimes it is useful to prevent this,
-        match,  or  to  cause it fail earlier than it otherwise might, when the
+        either to change the nature of the match, or to cause it  fail  earlier
-        author of the pattern knows there is no point in carrying on.
+        than  it otherwise might, when the author of the pattern knows there is
+        no point in carrying on.
         Consider, for example, the pattern \d+foo when applied to  the  subject
         line
-Line 3245 
 ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
+Line 3845 
 ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
         the  means for specifying that once a subpattern has matched, it is not
         to be re-evaluated in this way.
-        If we use atomic grouping for the previous example, the  matcher  would
+        If we use atomic grouping for the previous example, the  matcher  gives
-        give up immediately on failing to match "foo" the first time. The nota-
+        up  immediately  on failing to match "foo" the first time. The notation
-        tion is a kind of special parenthesis, starting with  (?>  as  in  this
+        is a kind of special parenthesis, starting with (?> as in this example:
-        example:
           (?>\d+)foo
-Line 3280 
 ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
+Line 3879 
 ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
         Possessive  quantifiers  are  always  greedy;  the   setting   of   the
         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
         simpler forms of atomic group. However, there is no difference  in  the
-        meaning  or  processing  of  a possessive quantifier and the equivalent
+        meaning  of  a  possessive  quantifier and the equivalent atomic group,
-        atomic group.
+        though there may be a performance  difference;  possessive  quantifiers
+        should be slightly faster.
-        The possessive quantifier syntax is an extension to the Perl syntax. It
-        originates in Sun's Java package.
+        The  possessive  quantifier syntax is an extension to the Perl 5.8 syn-
+        tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first
-        When  a  pattern  contains an unlimited repeat inside a subpattern that
+        edition of his book. Mike McCloskey liked it, so implemented it when he
-        can itself be repeated an unlimited number of  times,  the  use  of  an
+        built Sun's Java package, and PCRE copied it from there. It  ultimately
-        atomic  group  is  the  only way to avoid some failing matches taking a
+        found its way into Perl at release 5.10.
+        PCRE has an optimization that automatically "possessifies" certain sim-
+        ple pattern constructs. For example, the sequence  A+B  is  treated  as
+        A++B  because  there is no point in backtracking into a sequence of A's
+        when B must follow.
+        When a pattern contains an unlimited repeat inside  a  subpattern  that
+        can  itself  be  repeated  an  unlimited number of times, the use of an
+        atomic group is the only way to avoid some  failing  matches  taking  a
         very long time indeed. The pattern
           (\D+|<\d+>)*[!?]
-        matches an unlimited number of substrings that either consist  of  non-
+        matches  an  unlimited number of substrings that either consist of non-
-        digits,  or  digits  enclosed in <>, followed by either ! or ?. When it
+        digits, or digits enclosed in <>, followed by either ! or  ?.  When  it
         matches, it runs quickly. However, if it is applied to
           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
-        it takes a long time before reporting  failure.  This  is  because  the
+        it  takes  a  long  time  before reporting failure. This is because the
-        string  can be divided between the internal \D+ repeat and the external
+        string can be divided between the internal \D+ repeat and the  external
-        * repeat in a large number of ways, and all  have  to  be  tried.  (The
+        *  repeat  in  a  large  number of ways, and all have to be tried. (The
-        example  uses  [!?]  rather than a single character at the end, because
+        example uses [!?] rather than a single character at  the  end,  because
-        both PCRE and Perl have an optimization that allows  for  fast  failure
+        both  PCRE  and  Perl have an optimization that allows for fast failure
-        when  a single character is used. They remember the last single charac-
+        when a single character is used. They remember the last single  charac-
-        ter that is required for a match, and fail early if it is  not  present
+        ter  that  is required for a match, and fail early if it is not present
-        in  the  string.)  If  the pattern is changed so that it uses an atomic
+        in the string.) If the pattern is changed so that  it  uses  an  atomic
         group, like this:
           ((?>\D+)|<\d+>)*[!?]
-        sequences of non-digits cannot be broken, and failure happens  quickly.
+        sequences  of non-digits cannot be broken, and failure happens quickly.
  BACK REFERENCES
         Outside a character class, a backslash followed by a digit greater than
 (and possibly further digits) is a back reference to a capturing sub-
-        pattern  earlier  (that is, to its left) in the pattern, provided there
+        pattern earlier (that is, to its left) in the pattern,  provided  there
         have been that many previous capturing left parentheses.
         However, if the decimal number following the backslash is less than 10,
-        it  is  always  taken  as a back reference, and causes an error only if
+        it is always taken as a back reference, and causes  an  error  only  if
-        there are not that many capturing left parentheses in the  entire  pat-
+        there  are  not that many capturing left parentheses in the entire pat-
-        tern.  In  other words, the parentheses that are referenced need not be
+        tern. In other words, the parentheses that are referenced need  not  be
-        to the left of the reference for numbers less than 10. See the  subsec-
+        to  the left of the reference for numbers less than 10. A "forward back
-        tion  entitled  "Non-printing  characters" above for further details of
+        reference" of this type can make sense when a  repetition  is  involved
-        the handling of digits following a backslash.
+        and  the  subpattern to the right has participated in an earlier itera-
+        tion.
-        A back reference matches whatever actually matched the  capturing  sub-
+        It is not possible to have a numerical "forward back  reference"  to  a
-        pattern  in  the  current subject string, rather than anything matching
+        subpattern  whose  number  is  10  or  more using this syntax because a
+        sequence such as \50 is interpreted as a character  defined  in  octal.
+        See the subsection entitled "Non-printing characters" above for further
+        details of the handling of digits following a backslash.  There  is  no
+        such  problem  when named parentheses are used. A back reference to any
+        subpattern is possible using named parentheses (see below).
+        Another way of avoiding the ambiguity inherent in  the  use  of  digits
+        following a backslash is to use the \g escape sequence, which is a fea-
+        ture introduced in Perl 5.10. This escape must be followed by  a  posi-
+        tive  or  a negative number, optionally enclosed in braces. These exam-
+        ples are all identical:
+          (ring), \1
+          (ring), \g1
+          (ring), \g{1}
+        A positive number specifies an absolute reference without the ambiguity
+        that  is  present  in  the older syntax. It is also useful when literal
+        digits follow the reference. A negative number is a relative reference.
+        Consider this example:
+          (abc(def)ghi)\g{-1}
+        The sequence \g{-1} is a reference to the most recently started captur-
+        ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,
+        \g{-2} would be equivalent to \1. The use of relative references can be
+        helpful in long patterns, and also in  patterns  that  are  created  by
+        joining together fragments that contain references within themselves.
+        A  back  reference matches whatever actually matched the capturing sub-
+        pattern in the current subject string, rather  than  anything  matching
         the subpattern itself (see "Subpatterns as subroutines" below for a way
         of doing that). So the pattern
           (sens|respons)e and \1ibility
-        matches  "sense and sensibility" and "response and responsibility", but
+        matches "sense and sensibility" and "response and responsibility",  but
-        not "sense and responsibility". If caseful matching is in force at  the
+        not  "sense and responsibility". If caseful matching is in force at the
-        time  of the back reference, the case of letters is relevant. For exam-
+        time of the back reference, the case of letters is relevant. For  exam-
         ple,
           ((?i)rah)\s+\1
-        matches "rah rah" and "RAH RAH", but not "RAH  rah",  even  though  the
+        matches  "rah  rah"  and  "RAH RAH", but not "RAH rah", even though the
         original capturing subpattern is matched caselessly.
-        Back  references  to named subpatterns use the Python syntax (?P=name).
+        There are several different ways of writing back  references  to  named
-        We could rewrite the above example as follows:
+        subpatterns.  The  .NET syntax \k{name} and the Perl syntax \k<name> or
+        \k'name' are supported, as is the Python syntax (?P=name). Perl  5.10's
+        unified back reference syntax, in which \g can be used for both numeric
+        and named references, is also supported. We  could  rewrite  the  above
+        example in any of the following ways:
+          (?<p1>(?i)rah)\s+\k<p1>
+          (?'p1'(?i)rah)\s+\k{p1}
+          (?P<p1>(?i)rah)\s+(?P=p1)
+          (?<p1>(?i)rah)\s+\g{p1}
-          (?<p1>(?i)rah)\s+(?P=p1)
+        A  subpattern  that  is  referenced  by  name may appear in the pattern
+        before or after the reference.
         There may be more than one back reference to the same subpattern. If  a
         subpattern  has  not actually been used in a particular match, any back
-Line 3438 
 ASSERTIONS
+Line 4088 
 ASSERTIONS
         does  find  an  occurrence  of "bar" that is not preceded by "foo". The
         contents of a lookbehind assertion are restricted  such  that  all  the
         strings it matches must have a fixed length. However, if there are sev-
-        eral alternatives, they do not all have to have the same fixed  length.
+        eral top-level alternatives, they do not all  have  to  have  the  same
-        Thus
+        fixed length. Thus
           (?<=bullock|donkey)
-Line 3461 
 ASSERTIONS
+Line 4111 
 ASSERTIONS
           (?<=abc|abde)
+        In some cases, the Perl 5.10 escape sequence \K (see above) can be used
+        instead of a lookbehind assertion; this is not restricted to  a  fixed-
+        length.
         The  implementation  of lookbehind assertions is, for each alternative,
-        to temporarily move the current position back by the  fixed  width  and
+        to temporarily move the current position back by the fixed  length  and
         then try to match. If there are insufficient characters before the cur-
-        rent position, the match is deemed to fail.
+        rent position, the assertion fails.
         PCRE does not allow the \C escape (which matches a single byte in UTF-8
         mode)  to appear in lookbehind assertions, because it makes it impossi-
-        ble to calculate the length of the lookbehind. The \X escape, which can
+        ble to calculate the length of the lookbehind. The \X and  \R  escapes,
-        match different numbers of bytes, is also not permitted.
+        which can match different numbers of bytes, are also not permitted.
-        Atomic  groups can be used in conjunction with lookbehind assertions to
+        Possessive  quantifiers  can  be  used  in  conjunction with lookbehind
-        specify efficient matching at the end of the subject string. Consider a
+        assertions to specify efficient matching at  the  end  of  the  subject
-        simple pattern such as
+        string. Consider a simple pattern such as
           abcd$
-Line 3490 
 ASSERTIONS
+Line 4144 
 ASSERTIONS
         again  the search for "a" covers the entire string, from right to left,
         so we are no better off. However, if the pattern is written as
-          ^(?>.*)(?<=abcd)
-        or, equivalently, using the possessive quantifier syntax,
           ^.*+(?<=abcd)
-        there can be no backtracking for the .* item; it  can  match  only  the
+        there can be no backtracking for the .*+ item; it can  match  only  the
         entire  string.  The subsequent lookbehind assertion does a single test
         on the last four characters. If it fails, the match fails  immediately.
         For  long  strings, this approach makes a significant difference to the
-Line 3551 
 CONDITIONAL SUBPATTERNS
+Line 4201 
 CONDITIONAL SUBPATTERNS
         no-pattern (if present) is used. If there are more  than  two  alterna-
         tives in the subpattern, a compile-time error occurs.
-        There are three kinds of condition. If the text between the parentheses
+        There  are  four  kinds of condition: references to subpatterns, refer-
-        consists of a sequence of digits, the condition  is  satisfied  if  the
+        ences to recursion, a pseudo-condition called DEFINE, and assertions.
-        capturing  subpattern of that number has previously matched. The number
-        must be greater than zero. Consider the following pattern,  which  con-
+    Checking for a used subpattern by number
-        tains  non-significant white space to make it more readable (assume the
-        PCRE_EXTENDED option) and to divide it into three  parts  for  ease  of
+        If the text between the parentheses consists of a sequence  of  digits,
-        discussion:
+        the  condition  is  true if the capturing subpattern of that number has
+        previously matched. An alternative notation is to  precede  the  digits
+        with a plus or minus sign. In this case, the subpattern number is rela-
+        tive rather than absolute.  The most recently opened parentheses can be
+        referenced  by  (?(-1),  the  next most recent by (?(-2), and so on. In
+        looping constructs it can also make sense to refer to subsequent groups
+        with constructs such as (?(+2).
+        Consider  the  following  pattern, which contains non-significant white
+        space to make it more readable (assume the PCRE_EXTENDED option) and to
+        divide it into three parts for ease of discussion:
           ( \( )?    [^()]+    (?(1) \) )
-Line 3572 
 CONDITIONAL SUBPATTERNS
+Line 4232 
 CONDITIONAL SUBPATTERNS
         other  words,  this  pattern  matches  a  sequence  of non-parentheses,
         optionally enclosed in parentheses.
-        If the condition is the string (R), it is satisfied if a recursive call
+        If you were embedding this pattern in a larger one,  you  could  use  a
-        to  the pattern or subpattern has been made. At "top level", the condi-
+        relative reference:
-        tion is false.  This  is  a  PCRE  extension.  Recursive  patterns  are
-        described in the next section.
+          ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...
+        This  makes  the  fragment independent of the parentheses in the larger
+        pattern.
+    Checking for a used subpattern by name
+        Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a
+        used  subpattern  by  name.  For compatibility with earlier versions of
+        PCRE, which had this facility before Perl, the syntax  (?(name)...)  is
+        also  recognized. However, there is a possible ambiguity with this syn-
+        tax, because subpattern names may  consist  entirely  of  digits.  PCRE
+        looks  first for a named subpattern; if it cannot find one and the name
+        consists entirely of digits, PCRE looks for a subpattern of  that  num-
+        ber,  which must be greater than zero. Using subpattern names that con-
+        sist entirely of digits is not recommended.
-        If  the  condition  is  not  a sequence of digits or (R), it must be an
+        Rewriting the above example to use a named subpattern gives this:
+          (?<OPEN> \( )?    [^()]+    (?(<OPEN>) \) )
+    Checking for pattern recursion
+        If the condition is the string (R), and there is no subpattern with the
+        name  R, the condition is true if a recursive call to the whole pattern
+        or any subpattern has been made. If digits or a name preceded by amper-
+        sand follow the letter R, for example:
+          (?(R3)...) or (?(R&name)...)
+        the  condition is true if the most recent recursion is into the subpat-
+        tern whose number or name is given. This condition does not  check  the
+        entire recursion stack.
+        At  "top  level", all these recursion test conditions are false. Recur-
+        sive patterns are described below.
+    Defining subpatterns for use by reference only
+        If the condition is the string (DEFINE), and  there  is  no  subpattern
+        with  the  name  DEFINE,  the  condition is always false. In this case,
+        there may be only one alternative  in  the  subpattern.  It  is  always
+        skipped  if  control  reaches  this  point  in the pattern; the idea of
+        DEFINE is that it can be used to define "subroutines" that can be  ref-
+        erenced  from elsewhere. (The use of "subroutines" is described below.)
+        For example, a pattern to match an IPv4 address could be  written  like
+        this (ignore whitespace and line breaks):
+          (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )
+          \b (?&byte) (\.(?&byte)){3} \b
+        The  first part of the pattern is a DEFINE group inside which a another
+        group named "byte" is defined. This matches an individual component  of
+        an  IPv4  address  (a number less than 256). When matching takes place,
+        this part of the pattern is skipped because DEFINE acts  like  a  false
+        condition.
+        The rest of the pattern uses references to the named group to match the
+        four dot-separated components of an IPv4 address, insisting on  a  word
+        boundary at each end.
+    Assertion conditions
+        If  the  condition  is  not  in any of the above formats, it must be an
         assertion.  This may be a positive or negative lookahead or  lookbehind
         assertion.  Consider  this  pattern,  again  containing non-significant
         white space, and with the two alternatives on the second line:
-Line 3602 
 COMMENTS
+Line 4324 
 COMMENTS
         at all.
         If  the PCRE_EXTENDED option is set, an unescaped # character outside a
-        character class introduces a comment that continues up to the next new-
+        character class introduces a  comment  that  continues  to  immediately
-        line character in the pattern.
+        after the next newline in the pattern.
  RECURSIVE PATTERNS
-Line 3612 
 RECURSIVE PATTERNS
+Line 4334 
 RECURSIVE PATTERNS
         unlimited nested parentheses. Without the use of  recursion,  the  best
         that  can  be  done  is  to use a pattern that matches up to some fixed
         depth of nesting. It is not possible to  handle  an  arbitrary  nesting
-        depth.  Perl  provides  a  facility  that allows regular expressions to
+        depth.
-        recurse (amongst other things). It does this by interpolating Perl code
-        in the expression at run time, and the code can refer to the expression
+        For some time, Perl has provided a facility that allows regular expres-
-        itself. A Perl pattern to solve the parentheses problem can be  created
+        sions to recurse (amongst other things). It does this by  interpolating
-        like this:
+        Perl  code in the expression at run time, and the code can refer to the
+        expression itself. A Perl pattern using code interpolation to solve the
+        parentheses problem can be created like this:
           $re = qr{\( (?: (?>[^()]+) | (?p{$re}) )* \)}x;
         The (?p{...}) item interpolates Perl code at run time, and in this case
-        refers recursively to the pattern in which it appears. Obviously,  PCRE
+        refers recursively to the pattern in which it appears.
-        cannot  support  the  interpolation  of Perl code. Instead, it supports
-        some special syntax for recursion of the entire pattern, and  also  for
-        individual subpattern recursion.
-        The  special item that consists of (? followed by a number greater than
+        Obviously, PCRE cannot support the interpolation of Perl code. Instead,
+        it  supports  special  syntax  for recursion of the entire pattern, and
+        also for individual subpattern recursion.  After  its  introduction  in
+        PCRE  and  Python,  this  kind of recursion was introduced into Perl at
+        release 5.10.
+        A special item that consists of (? followed by a  number  greater  than
         zero and a closing parenthesis is a recursive call of the subpattern of
-        the  given  number, provided that it occurs inside that subpattern. (If
+        the given number, provided that it occurs inside that  subpattern.  (If
-        not, it is a "subroutine" call, which is described  in  the  next  sec-
+        not,  it  is  a  "subroutine" call, which is described in the next sec-
-        tion.)  The special item (?R) is a recursive call of the entire regular
+        tion.) The special item (?R) or (?0) is a recursive call of the  entire
-        expression.
+        regular expression.
+        In  PCRE (like Python, but unlike Perl), a recursive subpattern call is
+        always treated as an atomic group. That is, once it has matched some of
+        the subject string, it is never re-entered, even if it contains untried
+        alternatives and there is a subsequent matching failure.
-        For example, this PCRE pattern solves the  nested  parentheses  problem
+        This PCRE pattern solves the nested  parentheses  problem  (assume  the
-        (assume  the  PCRE_EXTENDED  option  is  set  so  that  white  space is
+        PCRE_EXTENDED option is set so that white space is ignored):
-        ignored):
           \( ( (?>[^()]+) | (?R) )* \)
-        First it matches an opening parenthesis. Then it matches any number  of
+        First  it matches an opening parenthesis. Then it matches any number of
-        substrings  which  can  either  be  a sequence of non-parentheses, or a
+        substrings which can either be a  sequence  of  non-parentheses,  or  a
-        recursive match of the pattern itself (that is  a  correctly  parenthe-
+        recursive  match  of the pattern itself (that is, a correctly parenthe-
         sized substring).  Finally there is a closing parenthesis.
-        If  this  were  part of a larger pattern, you would not want to recurse
+        If this were part of a larger pattern, you would not  want  to  recurse
         the entire pattern, so instead you could use this:
           ( \( ( (?>[^()]+) | (?1) )* \) )
-        We have put the pattern into parentheses, and caused the  recursion  to
+        We  have  put the pattern into parentheses, and caused the recursion to
-        refer  to them instead of the whole pattern. In a larger pattern, keep-
+        refer to them instead of the whole pattern.
-        ing track of parenthesis numbers can be tricky. It may be  more  conve-
-        nient  to use named parentheses instead. For this, PCRE uses (?P>name),
+        In a larger pattern,  keeping  track  of  parenthesis  numbers  can  be
-        which is an extension to the Python syntax that  PCRE  uses  for  named
+        tricky.  This is made easier by the use of relative references. (A Perl
-        parentheses (Perl does not provide named parentheses). We could rewrite
+.10 feature.)  Instead of (?1) in the  pattern  above  you  can  write
-        the above example as follows:
+        (?-2) to refer to the second most recently opened parentheses preceding
+        the recursion. In other  words,  a  negative  number  counts  capturing
-          (?P<pn> \( ( (?>[^()]+) | (?P>pn) )* \) )
+        parentheses leftwards from the point at which it is encountered.
-        This particular example pattern contains nested unlimited repeats,  and
+        It  is  also  possible  to refer to subsequently opened parentheses, by
-        so  the  use of atomic grouping for matching strings of non-parentheses
+        writing references such as (?+2). However, these  cannot  be  recursive
-        is important when applying the pattern to strings that  do  not  match.
+        because  the  reference  is  not inside the parentheses that are refer-
-        For example, when this pattern is applied to
+        enced. They are always "subroutine" calls, as  described  in  the  next
+        section.
+        An  alternative  approach is to use named parentheses instead. The Perl
+        syntax for this is (?&name); PCRE's earlier syntax  (?P>name)  is  also
+        supported. We could rewrite the above example as follows:
+          (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )
+        If  there  is more than one subpattern with the same name, the earliest
+        one is used.
+        This particular example pattern that we have been looking  at  contains
+        nested  unlimited repeats, and so the use of atomic grouping for match-
+        ing strings of non-parentheses is important when applying  the  pattern
+        to strings that do not match. For example, when this pattern is applied
+        to
           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
-        it  yields "no match" quickly. However, if atomic grouping is not used,
+        it yields "no match" quickly. However, if atomic grouping is not  used,
-        the match runs for a very long time indeed because there  are  so  many
+        the  match  runs  for a very long time indeed because there are so many
-        different  ways  the  + and * repeats can carve up the subject, and all
+        different ways the + and * repeats can carve up the  subject,  and  all
         have to be tested before failure can be reported.
         At the end of a match, the values set for any capturing subpatterns are
         those from the outermost level of the recursion at which the subpattern
-        value is set.  If you want to obtain  intermediate  values,  a  callout
+        value  is  set.   If  you want to obtain intermediate values, a callout