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revision 394 by ph10, Wed Mar 18 16:38:23 2009 UTC revision 517 by ph10, Wed May 5 10:44:20 2010 UTC
# Line 21  published by O'Reilly, covers regular ex Line 21  published by O'Reilly, covers regular ex
21  description of PCRE's regular expressions is intended as reference material.  description of PCRE's regular expressions is intended as reference material.
22  .P  .P
23  The original operation of PCRE was on strings of one-byte characters. However,  The original operation of PCRE was on strings of one-byte characters. However,
24  there is now also support for UTF-8 character strings. To use this, you must  there is now also support for UTF-8 character strings. To use this,
25  build PCRE to include UTF-8 support, and then call \fBpcre_compile()\fP with  PCRE must be built to include UTF-8 support, and you must call
26  the PCRE_UTF8 option. How this affects pattern matching is mentioned in several  \fBpcre_compile()\fP or \fBpcre_compile2()\fP with the PCRE_UTF8 option. There
27  places below. There is also a summary of UTF-8 features in the  is also a special sequence that can be given at the start of a pattern:
28    .sp
29      (*UTF8)
30    .sp
31    Starting a pattern with this sequence is equivalent to setting the PCRE_UTF8
32    option. This feature is not Perl-compatible. How setting UTF-8 mode affects
33    pattern matching is mentioned in several places below. There is also a summary
34    of UTF-8 features in the
35  .\" HTML <a href="pcre.html#utf8support">  .\" HTML <a href="pcre.html#utf8support">
36  .\" </a>  .\" </a>
37  section on UTF-8 support  section on UTF-8 support
# Line 76  string with one of the following five se Line 83  string with one of the following five se
83    (*ANYCRLF)   any of the three above    (*ANYCRLF)   any of the three above
84    (*ANY)       all Unicode newline sequences    (*ANY)       all Unicode newline sequences
85  .sp  .sp
86  These override the default and the options given to \fBpcre_compile()\fP. For  These override the default and the options given to \fBpcre_compile()\fP or
87  example, on a Unix system where LF is the default newline sequence, the pattern  \fBpcre_compile2()\fP. For example, on a Unix system where LF is the default
88    newline sequence, the pattern
89  .sp  .sp
90    (*CR)a.b    (*CR)a.b
91  .sp  .sp
# Line 87  Perl-compatible, are recognized only at Line 95  Perl-compatible, are recognized only at
95  they must be in upper case. If more than one of them is present, the last one  they must be in upper case. If more than one of them is present, the last one
96  is used.  is used.
97  .P  .P
98  The newline convention does not affect what the \eR escape sequence matches. By  The newline convention affects the interpretation of the dot metacharacter when
99  default, this is any Unicode newline sequence, for Perl compatibility. However,  PCRE_DOTALL is not set, and also the behaviour of \eN. However, it does not
100  this can be changed; see the description of \eR in the section entitled  affect what the \eR escape sequence matches. By default, this is any Unicode
101    newline sequence, for Perl compatibility. However, this can be changed; see the
102    description of \eR in the section entitled
103  .\" HTML <a href="#newlineseq">  .\" HTML <a href="#newlineseq">
104  .\" </a>  .\" </a>
105  "Newline sequences"  "Newline sequences"
# Line 199  The \eQ...\eE sequence is recognized bot Line 209  The \eQ...\eE sequence is recognized bot
209  A second use of backslash provides a way of encoding non-printing characters  A second use of backslash provides a way of encoding non-printing characters
210  in patterns in a visible manner. There is no restriction on the appearance of  in patterns in a visible manner. There is no restriction on the appearance of
211  non-printing characters, apart from the binary zero that terminates a pattern,  non-printing characters, apart from the binary zero that terminates a pattern,
212  but when a pattern is being prepared by text editing, it is usually easier to  but when a pattern is being prepared by text editing, it is often easier to use
213  use one of the following escape sequences than the binary character it  one of the following escape sequences than the binary character it represents:
 represents:  
214  .sp  .sp
215    \ea        alarm, that is, the BEL character (hex 07)    \ea        alarm, that is, the BEL character (hex 07)
216    \ecx       "control-x", where x is any character    \ecx       "control-x", where x is any character
# Line 210  represents: Line 219  represents:
219    \en        linefeed (hex 0A)    \en        linefeed (hex 0A)
220    \er        carriage return (hex 0D)    \er        carriage return (hex 0D)
221    \et        tab (hex 09)    \et        tab (hex 09)
222    \eddd      character with octal code ddd, or backreference    \eddd      character with octal code ddd, or back reference
223    \exhh      character with hex code hh    \exhh      character with hex code hh
224    \ex{hhh..} character with hex code hhh..    \ex{hhh..} character with hex code hhh..
225  .sp  .sp
# Line 288  zero, because no more than three octal d Line 297  zero, because no more than three octal d
297  .P  .P
298  All the sequences that define a single character value can be used both inside  All the sequences that define a single character value can be used both inside
299  and outside character classes. In addition, inside a character class, the  and outside character classes. In addition, inside a character class, the
300  sequence \eb is interpreted as the backspace character (hex 08), and the  sequence \eb is interpreted as the backspace character (hex 08). The sequences
301  sequences \eR and \eX are interpreted as the characters "R" and "X",  \eB, \eN, \eR, and \eX are not special inside a character class. Like any other
302  respectively. Outside a character class, these sequences have different  unrecognized escape sequences, they are treated as the literal characters "B",
303  meanings  "N", "R", and "X" by default, but cause an error if the PCRE_EXTRA option is
304  .\" HTML <a href="#uniextseq">  set. Outside a character class, these sequences have different meanings.
 .\" </a>  
 (see below).  
 .\"  
305  .  .
306  .  .
307  .SS "Absolute and relative back references"  .SS "Absolute and relative back references"
# Line 326  syntax for referencing a subpattern as a Line 332  syntax for referencing a subpattern as a
332  later.  later.
333  .\"  .\"
334  Note that \eg{...} (Perl syntax) and \eg<...> (Oniguruma syntax) are \fInot\fP  Note that \eg{...} (Perl syntax) and \eg<...> (Oniguruma syntax) are \fInot\fP
335  synonymous. The former is a back reference; the latter is a subroutine call.  synonymous. The former is a back reference; the latter is a
336    .\" HTML <a href="#subpatternsassubroutines">
337    .\" </a>
338    subroutine
339    .\"
340    call.
341  .  .
342  .  .
343  .SS "Generic character types"  .SS "Generic character types"
344  .rs  .rs
345  .sp  .sp
346  Another use of backslash is for specifying generic character types. The  Another use of backslash is for specifying generic character types:
 following are always recognized:  
347  .sp  .sp
348    \ed     any decimal digit    \ed     any decimal digit
349    \eD     any character that is not a decimal digit    \eD     any character that is not a decimal digit
# Line 346  following are always recognized: Line 356  following are always recognized:
356    \ew     any "word" character    \ew     any "word" character
357    \eW     any "non-word" character    \eW     any "non-word" character
358  .sp  .sp
359  Each pair of escape sequences partitions the complete set of characters into  There is also the single sequence \eN, which matches a non-newline character.
360  two disjoint sets. Any given character matches one, and only one, of each pair.  This is the same as
361    .\" HTML <a href="#fullstopdot">
362    .\" </a>
363    the "." metacharacter
364    .\"
365    when PCRE_DOTALL is not set.
366    .P
367    Each pair of lower and upper case escape sequences partitions the complete set
368    of characters into two disjoint sets. Any given character matches one, and only
369    one, of each pair.
370  .P  .P
371  These character type sequences can appear both inside and outside character  These character type sequences can appear both inside and outside character
372  classes. They each match one character of the appropriate type. If the current  classes. They each match one character of the appropriate type. If the current
# Line 364  In UTF-8 mode, characters with values gr Line 383  In UTF-8 mode, characters with values gr
383  \ew, and always match \eD, \eS, and \eW. This is true even when Unicode  \ew, and always match \eD, \eS, and \eW. This is true even when Unicode
384  character property support is available. These sequences retain their original  character property support is available. These sequences retain their original
385  meanings from before UTF-8 support was available, mainly for efficiency  meanings from before UTF-8 support was available, mainly for efficiency
386  reasons. Note that this also affects \eb, because it is defined in terms of \ew  reasons. Note that this also affects \eb, because it is defined in terms of \ew
387  and \eW.  and \eW.
388  .P  .P
389  The sequences \eh, \eH, \ev, and \eV are Perl 5.10 features. In contrast to the  The sequences \eh, \eH, \ev, and \eV are Perl 5.10 features. In contrast to the
# Line 456  one of the following sequences: Line 475  one of the following sequences:
475    (*BSR_ANYCRLF)   CR, LF, or CRLF only    (*BSR_ANYCRLF)   CR, LF, or CRLF only
476    (*BSR_UNICODE)   any Unicode newline sequence    (*BSR_UNICODE)   any Unicode newline sequence
477  .sp  .sp
478  These override the default and the options given to \fBpcre_compile()\fP, but  These override the default and the options given to \fBpcre_compile()\fP or
479  they can be overridden by options given to \fBpcre_exec()\fP. Note that these  \fBpcre_compile2()\fP, but they can be overridden by options given to
480  special settings, which are not Perl-compatible, are recognized only at the  \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP. Note that these special settings,
481  very start of a pattern, and that they must be in upper case. If more than one  which are not Perl-compatible, are recognized only at the very start of a
482  of them is present, the last one is used. They can be combined with a change of  pattern, and that they must be in upper case. If more than one of them is
483  newline convention, for example, a pattern can start with:  present, the last one is used. They can be combined with a change of newline
484    convention, for example, a pattern can start with:
485  .sp  .sp
486    (*ANY)(*BSR_ANYCRLF)    (*ANY)(*BSR_ANYCRLF)
487  .sp  .sp
488  Inside a character class, \eR matches the letter "R".  Inside a character class, \eR is treated as an unrecognized escape sequence,
489    and so matches the letter "R" by default, but causes an error if PCRE_EXTRA is
490    set.
491  .  .
492  .  .
493  .\" HTML <a name="uniextseq"></a>  .\" HTML <a name="uniextseq"></a>
# Line 483  The extra escape sequences are: Line 505  The extra escape sequences are:
505    \eX       an extended Unicode sequence    \eX       an extended Unicode sequence
506  .sp  .sp
507  The property names represented by \fIxx\fP above are limited to the Unicode  The property names represented by \fIxx\fP above are limited to the Unicode
508  script names, the general category properties, and "Any", which matches any  script names, the general category properties, "Any", which matches any
509  character (including newline). Other properties such as "InMusicalSymbols" are  character (including newline), and some special PCRE properties (described
510  not currently supported by PCRE. Note that \eP{Any} does not match any  in the
511  characters, so always causes a match failure.  .\" HTML <a href="#extraprops">
512    .\" </a>
513    next section).
514    .\"
515    Other Perl properties such as "InMusicalSymbols" are not currently supported by
516    PCRE. Note that \eP{Any} does not match any characters, so always causes a
517    match failure.
518  .P  .P
519  Sets of Unicode characters are defined as belonging to certain scripts. A  Sets of Unicode characters are defined as belonging to certain scripts. A
520  character from one of these sets can be matched using a script name. For  character from one of these sets can be matched using a script name. For
# Line 500  Those that are not part of an identified Line 528  Those that are not part of an identified
528  .P  .P
529  Arabic,  Arabic,
530  Armenian,  Armenian,
531    Avestan,
532  Balinese,  Balinese,
533    Bamum,
534  Bengali,  Bengali,
535  Bopomofo,  Bopomofo,
536  Braille,  Braille,
537  Buginese,  Buginese,
538  Buhid,  Buhid,
539  Canadian_Aboriginal,  Canadian_Aboriginal,
540    Carian,
541    Cham,
542  Cherokee,  Cherokee,
543  Common,  Common,
544  Coptic,  Coptic,
# Line 515  Cypriot, Line 547  Cypriot,
547  Cyrillic,  Cyrillic,
548  Deseret,  Deseret,
549  Devanagari,  Devanagari,
550    Egyptian_Hieroglyphs,
551  Ethiopic,  Ethiopic,
552  Georgian,  Georgian,
553  Glagolitic,  Glagolitic,
# Line 527  Hangul, Line 560  Hangul,
560  Hanunoo,  Hanunoo,
561  Hebrew,  Hebrew,
562  Hiragana,  Hiragana,
563    Imperial_Aramaic,
564  Inherited,  Inherited,
565    Inscriptional_Pahlavi,
566    Inscriptional_Parthian,
567    Javanese,
568    Kaithi,
569  Kannada,  Kannada,
570  Katakana,  Katakana,
571    Kayah_Li,
572  Kharoshthi,  Kharoshthi,
573  Khmer,  Khmer,
574  Lao,  Lao,
575  Latin,  Latin,
576    Lepcha,
577  Limbu,  Limbu,
578  Linear_B,  Linear_B,
579    Lisu,
580    Lycian,
581    Lydian,
582  Malayalam,  Malayalam,
583    Meetei_Mayek,
584  Mongolian,  Mongolian,
585  Myanmar,  Myanmar,
586  New_Tai_Lue,  New_Tai_Lue,
# Line 544  Nko, Line 588  Nko,
588  Ogham,  Ogham,
589  Old_Italic,  Old_Italic,
590  Old_Persian,  Old_Persian,
591    Old_South_Arabian,
592    Old_Turkic,
593    Ol_Chiki,
594  Oriya,  Oriya,
595  Osmanya,  Osmanya,
596  Phags_Pa,  Phags_Pa,
597  Phoenician,  Phoenician,
598    Rejang,
599  Runic,  Runic,
600    Samaritan,
601    Saurashtra,
602  Shavian,  Shavian,
603  Sinhala,  Sinhala,
604    Sundanese,
605  Syloti_Nagri,  Syloti_Nagri,
606  Syriac,  Syriac,
607  Tagalog,  Tagalog,
608  Tagbanwa,  Tagbanwa,
609  Tai_Le,  Tai_Le,
610    Tai_Tham,
611    Tai_Viet,
612  Tamil,  Tamil,
613  Telugu,  Telugu,
614  Thaana,  Thaana,
# Line 563  Thai, Line 616  Thai,
616  Tibetan,  Tibetan,
617  Tifinagh,  Tifinagh,
618  Ugaritic,  Ugaritic,
619    Vai,
620  Yi.  Yi.
621  .P  .P
622  Each character has exactly one general category property, specified by a  Each character has exactly one Unicode general category property, specified by
623  two-letter abbreviation. For compatibility with Perl, negation can be specified  a two-letter abbreviation. For compatibility with Perl, negation can be
624  by including a circumflex between the opening brace and the property name. For  specified by including a circumflex between the opening brace and the property
625  example, \ep{^Lu} is the same as \eP{Lu}.  name. For example, \ep{^Lu} is the same as \eP{Lu}.
626  .P  .P
627  If only one letter is specified with \ep or \eP, it includes all the general  If only one letter is specified with \ep or \eP, it includes all the general
628  category properties that start with that letter. In this case, in the absence  category properties that start with that letter. In this case, in the absence
# Line 635  cannot be tested by PCRE, unless UTF-8 v Line 689  cannot be tested by PCRE, unless UTF-8 v
689  .\" HREF  .\" HREF
690  \fBpcreapi\fP  \fBpcreapi\fP
691  .\"  .\"
692  page).  page). Perl does not support the Cs property.
693  .P  .P
694  The long synonyms for these properties that Perl supports (such as \ep{Letter})  The long synonyms for property names that Perl supports (such as \ep{Letter})
695  are not supported by PCRE, nor is it permitted to prefix any of these  are not supported by PCRE, nor is it permitted to prefix any of these
696  properties with "Is".  properties with "Is".
697  .P  .P
# Line 670  why the traditional escape sequences suc Line 724  why the traditional escape sequences suc
724  properties in PCRE.  properties in PCRE.
725  .  .
726  .  .
727    .\" HTML <a name="extraprops"></a>
728    .SS PCRE's additional properties
729    .rs
730    .sp
731    As well as the standard Unicode properties described in the previous
732    section, PCRE supports four more that make it possible to convert traditional
733    escape sequences such as \ew and \es and POSIX character classes to use Unicode
734    properties. These are:
735    .sp
736      Xan   Any alphanumeric character
737      Xps   Any POSIX space character
738      Xsp   Any Perl space character
739      Xwd   Any Perl "word" character
740    .sp
741    Xan matches characters that have either the L (letter) or the N (number)
742    property. Xps matches the characters tab, linefeed, vertical tab, formfeed, or
743    carriage return, and any other character that has the Z (separator) property.
744    Xsp is the same as Xps, except that vertical tab is excluded. Xwd matches the
745    same characters as Xan, plus underscore.
746    .
747    .
748  .\" HTML <a name="resetmatchstart"></a>  .\" HTML <a name="resetmatchstart"></a>
749  .SS "Resetting the match start"  .SS "Resetting the match start"
750  .rs  .rs
# Line 698  For example, when the pattern Line 773  For example, when the pattern
773    (foo)\eKbar    (foo)\eKbar
774  .sp  .sp
775  matches "foobar", the first substring is still set to "foo".  matches "foobar", the first substring is still set to "foo".
776    .P
777    Perl documents that the use of \eK within assertions is "not well defined". In
778    PCRE, \eK is acted upon when it occurs inside positive assertions, but is
779    ignored in negative assertions.
780  .  .
781  .  .
782  .\" HTML <a name="smallassertions"></a>  .\" HTML <a name="smallassertions"></a>
# Line 722  The backslashed assertions are: Line 801  The backslashed assertions are:
801    \ez     matches only at the end of the subject    \ez     matches only at the end of the subject
802    \eG     matches at the first matching position in the subject    \eG     matches at the first matching position in the subject
803  .sp  .sp
804  These assertions may not appear in character classes (but note that \eb has a  Inside a character class, \eb has a different meaning; it matches the backspace
805  different meaning, namely the backspace character, inside a character class).  character. If any other of these assertions appears in a character class, by
806    default it matches the corresponding literal character (for example, \eB
807    matches the letter B). However, if the PCRE_EXTRA option is set, an "invalid
808    escape sequence" error is generated instead.
809  .P  .P
810  A word boundary is a position in the subject string where the current character  A word boundary is a position in the subject string where the current character
811  and the previous character do not both match \ew or \eW (i.e. one matches  and the previous character do not both match \ew or \eW (i.e. one matches
812  \ew and the other matches \eW), or the start or end of the string if the  \ew and the other matches \eW), or the start or end of the string if the
813  first or last character matches \ew, respectively.  first or last character matches \ew, respectively. Neither PCRE nor Perl has a
814    separte "start of word" or "end of word" metasequence. However, whatever
815    follows \eb normally determines which it is. For example, the fragment
816    \eba matches "a" at the start of a word.
817  .P  .P
818  The \eA, \eZ, and \ez assertions differ from the traditional circumflex and  The \eA, \eZ, and \ez assertions differ from the traditional circumflex and
819  dollar (described in the next section) in that they only ever match at the very  dollar (described in the next section) in that they only ever match at the very
# Line 812  end of the subject in both modes, and if Line 897  end of the subject in both modes, and if
897  \eA it is always anchored, whether or not PCRE_MULTILINE is set.  \eA it is always anchored, whether or not PCRE_MULTILINE is set.
898  .  .
899  .  .
900  .SH "FULL STOP (PERIOD, DOT)"  .\" HTML <a name="fullstopdot"></a>
901    .SH "FULL STOP (PERIOD, DOT) AND \eN"
902  .rs  .rs
903  .sp  .sp
904  Outside a character class, a dot in the pattern matches any one character in  Outside a character class, a dot in the pattern matches any one character in
# Line 834  to match it. Line 920  to match it.
920  The handling of dot is entirely independent of the handling of circumflex and  The handling of dot is entirely independent of the handling of circumflex and
921  dollar, the only relationship being that they both involve newlines. Dot has no  dollar, the only relationship being that they both involve newlines. Dot has no
922  special meaning in a character class.  special meaning in a character class.
923    .P
924    The escape sequence \eN always behaves as a dot does when PCRE_DOTALL is not
925    set. In other words, it matches any one character except one that signifies the
926    end of a line.
927  .  .
928  .  .
929  .SH "MATCHING A SINGLE BYTE"  .SH "MATCHING A SINGLE BYTE"
# Line 860  the lookbehind. Line 950  the lookbehind.
950  .rs  .rs
951  .sp  .sp
952  An opening square bracket introduces a character class, terminated by a closing  An opening square bracket introduces a character class, terminated by a closing
953  square bracket. A closing square bracket on its own is not special. If a  square bracket. A closing square bracket on its own is not special by default.
954  closing square bracket is required as a member of the class, it should be the  However, if the PCRE_JAVASCRIPT_COMPAT option is set, a lone closing square
955  first data character in the class (after an initial circumflex, if present) or  bracket causes a compile-time error. If a closing square bracket is required as
956  escaped with a backslash.  a member of the class, it should be the first data character in the class
957    (after an initial circumflex, if present) or escaped with a backslash.
958  .P  .P
959  A character class matches a single character in the subject. In UTF-8 mode, the  A character class matches a single character in the subject. In UTF-8 mode, the
960  character may occupy more than one byte. A matched character must be in the set  character may be more than one byte long. A matched character must be in the
961  of characters defined by the class, unless the first character in the class  set of characters defined by the class, unless the first character in the class
962  definition is a circumflex, in which case the subject character must not be in  definition is a circumflex, in which case the subject character must not be in
963  the set defined by the class. If a circumflex is actually required as a member  the set defined by the class. If a circumflex is actually required as a member
964  of the class, ensure it is not the first character, or escape it with a  of the class, ensure it is not the first character, or escape it with a
# Line 877  For example, the character class [aeiou] Line 968  For example, the character class [aeiou]
968  [^aeiou] matches any character that is not a lower case vowel. Note that a  [^aeiou] matches any character that is not a lower case vowel. Note that a
969  circumflex is just a convenient notation for specifying the characters that  circumflex is just a convenient notation for specifying the characters that
970  are in the class by enumerating those that are not. A class that starts with a  are in the class by enumerating those that are not. A class that starts with a
971  circumflex is not an assertion: it still consumes a character from the subject  circumflex is not an assertion; it still consumes a character from the subject
972  string, and therefore it fails if the current pointer is at the end of the  string, and therefore it fails if the current pointer is at the end of the
973  string.  string.
974  .P  .P
# Line 891  caseful version would. In UTF-8 mode, PC Line 982  caseful version would. In UTF-8 mode, PC
982  case for characters whose values are less than 128, so caseless matching is  case for characters whose values are less than 128, so caseless matching is
983  always possible. For characters with higher values, the concept of case is  always possible. For characters with higher values, the concept of case is
984  supported if PCRE is compiled with Unicode property support, but not otherwise.  supported if PCRE is compiled with Unicode property support, but not otherwise.
985  If you want to use caseless matching for characters 128 and above, you must  If you want to use caseless matching in UTF8-mode for characters 128 and above,
986  ensure that PCRE is compiled with Unicode property support as well as with  you must ensure that PCRE is compiled with Unicode property support as well as
987  UTF-8 support.  with UTF-8 support.
988  .P  .P
989  Characters that might indicate line breaks are never treated in any special way  Characters that might indicate line breaks are never treated in any special way
990  when matching character classes, whatever line-ending sequence is in use, and  when matching character classes, whatever line-ending sequence is in use, and
# Line 1032  The PCRE-specific options PCRE_DUPNAMES, Line 1123  The PCRE-specific options PCRE_DUPNAMES,
1123  changed in the same way as the Perl-compatible options by using the characters  changed in the same way as the Perl-compatible options by using the characters
1124  J, U and X respectively.  J, U and X respectively.
1125  .P  .P
1126  When an option change occurs at top level (that is, not inside subpattern  When one of these option changes occurs at top level (that is, not inside
1127  parentheses), the change applies to the remainder of the pattern that follows.  subpattern parentheses), the change applies to the remainder of the pattern
1128  If the change is placed right at the start of a pattern, PCRE extracts it into  that follows. If the change is placed right at the start of a pattern, PCRE
1129  the global options (and it will therefore show up in data extracted by the  extracts it into the global options (and it will therefore show up in data
1130  \fBpcre_fullinfo()\fP function).  extracted by the \fBpcre_fullinfo()\fP function).
1131  .P  .P
1132  An option change within a subpattern (see below for a description of  An option change within a subpattern (see below for a description of
1133  subpatterns) affects only that part of the current pattern that follows it, so  subpatterns) affects only that part of the current pattern that follows it, so
# Line 1057  behaviour otherwise. Line 1148  behaviour otherwise.
1148  .P  .P
1149  \fBNote:\fP There are other PCRE-specific options that can be set by the  \fBNote:\fP There are other PCRE-specific options that can be set by the
1150  application when the compile or match functions are called. In some cases the  application when the compile or match functions are called. In some cases the
1151  pattern can contain special leading sequences to override what the application  pattern can contain special leading sequences such as (*CRLF) to override what
1152  has set or what has been defaulted. Details are given in the section entitled  the application has set or what has been defaulted. Details are given in the
1153    section entitled
1154  .\" HTML <a href="#newlineseq">  .\" HTML <a href="#newlineseq">
1155  .\" </a>  .\" </a>
1156  "Newline sequences"  "Newline sequences"
1157  .\"  .\"
1158  above.  above. There is also the (*UTF8) leading sequence that can be used to set UTF-8
1159    mode; this is equivalent to setting the PCRE_UTF8 option.
1160  .  .
1161  .  .
1162  .\" HTML <a name="subpattern"></a>  .\" HTML <a name="subpattern"></a>
# Line 1118  is reached, an option setting in one bra Line 1211  is reached, an option setting in one bra
1211  the above patterns match "SUNDAY" as well as "Saturday".  the above patterns match "SUNDAY" as well as "Saturday".
1212  .  .
1213  .  .
1214    .\" HTML <a name="dupsubpatternnumber"></a>
1215  .SH "DUPLICATE SUBPATTERN NUMBERS"  .SH "DUPLICATE SUBPATTERN NUMBERS"
1216  .rs  .rs
1217  .sp  .sp
# Line 1143  stored. Line 1237  stored.
1237    / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x    / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
1238    # 1            2         2  3        2     3     4    # 1            2         2  3        2     3     4
1239  .sp  .sp
1240  A backreference or a recursive call to a numbered subpattern always refers to  A back reference to a numbered subpattern uses the most recent value that is
1241  the first one in the pattern with the given number.  set for that number by any subpattern. The following pattern matches "abcabc"
1242    or "defdef":
1243    .sp
1244      /(?|(abc)|(def))\e1/
1245    .sp
1246    In contrast, a recursive or "subroutine" call to a numbered subpattern always
1247    refers to the first one in the pattern with the given number. The following
1248    pattern matches "abcabc" or "defabc":
1249    .sp
1250      /(?|(abc)|(def))(?1)/
1251    .sp
1252    If a
1253    .\" HTML <a href="#conditions">
1254    .\" </a>
1255    condition test
1256    .\"
1257    for a subpattern's having matched refers to a non-unique number, the test is
1258    true if any of the subpatterns of that number have matched.
1259  .P  .P
1260  An alternative approach to using this "branch reset" feature is to use  An alternative approach to using this "branch reset" feature is to use
1261  duplicate named subpatterns, as described in the next section.  duplicate named subpatterns, as described in the next section.
# Line 1159  if an expression is modified, the number Line 1270  if an expression is modified, the number
1270  difficulty, PCRE supports the naming of subpatterns. This feature was not  difficulty, PCRE supports the naming of subpatterns. This feature was not
1271  added to Perl until release 5.10. Python had the feature earlier, and PCRE  added to Perl until release 5.10. Python had the feature earlier, and PCRE
1272  introduced it at release 4.0, using the Python syntax. PCRE now supports both  introduced it at release 4.0, using the Python syntax. PCRE now supports both
1273  the Perl and the Python syntax.  the Perl and the Python syntax. Perl allows identically numbered subpatterns to
1274    have different names, but PCRE does not.
1275  .P  .P
1276  In PCRE, a subpattern can be named in one of three ways: (?<name>...) or  In PCRE, a subpattern can be named in one of three ways: (?<name>...) or
1277  (?'name'...) as in Perl, or (?P<name>...) as in Python. References to capturing  (?'name'...) as in Perl, or (?P<name>...) as in Python. References to capturing
1278  parentheses from other parts of the pattern, such as  parentheses from other parts of the pattern, such as
1279  .\" HTML <a href="#backreferences">  .\" HTML <a href="#backreferences">
1280  .\" </a>  .\" </a>
1281  backreferences,  back references,
1282  .\"  .\"
1283  .\" HTML <a href="#recursion">  .\" HTML <a href="#recursion">
1284  .\" </a>  .\" </a>
# Line 1186  extracting the name-to-number translatio Line 1298  extracting the name-to-number translatio
1298  is also a convenience function for extracting a captured substring by name.  is also a convenience function for extracting a captured substring by name.
1299  .P  .P
1300  By default, a name must be unique within a pattern, but it is possible to relax  By default, a name must be unique within a pattern, but it is possible to relax
1301  this constraint by setting the PCRE_DUPNAMES option at compile time. This can  this constraint by setting the PCRE_DUPNAMES option at compile time. (Duplicate
1302  be useful for patterns where only one instance of the named parentheses can  names are also always permitted for subpatterns with the same number, set up as
1303  match. Suppose you want to match the name of a weekday, either as a 3-letter  described in the previous section.) Duplicate names can be useful for patterns
1304  abbreviation or as the full name, and in both cases you want to extract the  where only one instance of the named parentheses can match. Suppose you want to
1305  abbreviation. This pattern (ignoring the line breaks) does the job:  match the name of a weekday, either as a 3-letter abbreviation or as the full
1306    name, and in both cases you want to extract the abbreviation. This pattern
1307    (ignoring the line breaks) does the job:
1308  .sp  .sp
1309    (?<DN>Mon|Fri|Sun)(?:day)?|    (?<DN>Mon|Fri|Sun)(?:day)?|
1310    (?<DN>Tue)(?:sday)?|    (?<DN>Tue)(?:sday)?|
# Line 1204  subpattern, as described in the previous Line 1318  subpattern, as described in the previous
1318  .P  .P
1319  The convenience function for extracting the data by name returns the substring  The convenience function for extracting the data by name returns the substring
1320  for the first (and in this example, the only) subpattern of that name that  for the first (and in this example, the only) subpattern of that name that
1321  matched. This saves searching to find which numbered subpattern it was. If you  matched. This saves searching to find which numbered subpattern it was.
1322  make a reference to a non-unique named subpattern from elsewhere in the  .P
1323  pattern, the one that corresponds to the lowest number is used. For further  If you make a back reference to a non-unique named subpattern from elsewhere in
1324  details of the interfaces for handling named subpatterns, see the  the pattern, the one that corresponds to the first occurrence of the name is
1325    used. In the absence of duplicate numbers (see the previous section) this is
1326    the one with the lowest number. If you use a named reference in a condition
1327    test (see the
1328    .\"
1329    .\" HTML <a href="#conditions">
1330    .\" </a>
1331    section about conditions
1332    .\"
1333    below), either to check whether a subpattern has matched, or to check for
1334    recursion, all subpatterns with the same name are tested. If the condition is
1335    true for any one of them, the overall condition is true. This is the same
1336    behaviour as testing by number. For further details of the interfaces for
1337    handling named subpatterns, see the
1338  .\" HREF  .\" HREF
1339  \fBpcreapi\fP  \fBpcreapi\fP
1340  .\"  .\"
1341  documentation.  documentation.
1342  .P  .P
1343  \fBWarning:\fP You cannot use different names to distinguish between two  \fBWarning:\fP You cannot use different names to distinguish between two
1344  subpatterns with the same number (see the previous section) because PCRE uses  subpatterns with the same number because PCRE uses only the numbers when
1345  only the numbers when matching.  matching. For this reason, an error is given at compile time if different names
1346    are given to subpatterns with the same number. However, you can give the same
1347    name to subpatterns with the same number, even when PCRE_DUPNAMES is not set.
1348  .  .
1349  .  .
1350  .SH REPETITION  .SH REPETITION
# Line 1233  items: Line 1362  items:
1362    a character class    a character class
1363    a back reference (see next section)    a back reference (see next section)
1364    a parenthesized subpattern (unless it is an assertion)    a parenthesized subpattern (unless it is an assertion)
1365      a recursive or "subroutine" call to a subpattern
1366  .sp  .sp
1367  The general repetition quantifier specifies a minimum and maximum number of  The general repetition quantifier specifies a minimum and maximum number of
1368  permitted matches, by giving the two numbers in curly brackets (braces),  permitted matches, by giving the two numbers in curly brackets (braces),
# Line 1343  worth setting PCRE_DOTALL in order to ob Line 1473  worth setting PCRE_DOTALL in order to ob
1473  alternatively using ^ to indicate anchoring explicitly.  alternatively using ^ to indicate anchoring explicitly.
1474  .P  .P
1475  However, there is one situation where the optimization cannot be used. When .*  However, there is one situation where the optimization cannot be used. When .*
1476  is inside capturing parentheses that are the subject of a backreference  is inside capturing parentheses that are the subject of a back reference
1477  elsewhere in the pattern, a match at the start may fail where a later one  elsewhere in the pattern, a match at the start may fail where a later one
1478  succeeds. Consider, for example:  succeeds. Consider, for example:
1479  .sp  .sp
# Line 1554  after the reference. Line 1684  after the reference.
1684  .P  .P
1685  There may be more than one back reference to the same subpattern. If a  There may be more than one back reference to the same subpattern. If a
1686  subpattern has not actually been used in a particular match, any back  subpattern has not actually been used in a particular match, any back
1687  references to it always fail. For example, the pattern  references to it always fail by default. For example, the pattern
1688  .sp  .sp
1689    (a|(bc))\e2    (a|(bc))\e2
1690  .sp  .sp
1691  always fails if it starts to match "a" rather than "bc". Because there may be  always fails if it starts to match "a" rather than "bc". However, if the
1692  many capturing parentheses in a pattern, all digits following the backslash are  PCRE_JAVASCRIPT_COMPAT option is set at compile time, a back reference to an
1693  taken as part of a potential back reference number. If the pattern continues  unset value matches an empty string.
1694  with a digit character, some delimiter must be used to terminate the back  .P
1695  reference. If the PCRE_EXTENDED option is set, this can be whitespace.  Because there may be many capturing parentheses in a pattern, all digits
1696  Otherwise an empty comment (see  following a backslash are taken as part of a potential back reference number.
1697    If the pattern continues with a digit character, some delimiter must be used to
1698    terminate the back reference. If the PCRE_EXTENDED option is set, this can be
1699    whitespace. Otherwise, the \eg{ syntax or an empty comment (see
1700  .\" HTML <a href="#comments">  .\" HTML <a href="#comments">
1701  .\" </a>  .\" </a>
1702  "Comments"  "Comments"
1703  .\"  .\"
1704  below) can be used.  below) can be used.
1705  .P  .
1706    .SS "Recursive back references"
1707    .rs
1708    .sp
1709  A back reference that occurs inside the parentheses to which it refers fails  A back reference that occurs inside the parentheses to which it refers fails
1710  when the subpattern is first used, so, for example, (a\e1) never matches.  when the subpattern is first used, so, for example, (a\e1) never matches.
1711  However, such references can be useful inside repeated subpatterns. For  However, such references can be useful inside repeated subpatterns. For
# Line 1583  to the previous iteration. In order for Line 1719  to the previous iteration. In order for
1719  that the first iteration does not need to match the back reference. This can be  that the first iteration does not need to match the back reference. This can be
1720  done using alternation, as in the example above, or by a quantifier with a  done using alternation, as in the example above, or by a quantifier with a
1721  minimum of zero.  minimum of zero.
1722    .P
1723    Back references of this type cause the group that they reference to be treated
1724    as an
1725    .\" HTML <a href="#atomicgroup">
1726    .\" </a>
1727    atomic group.
1728    .\"
1729    Once the whole group has been matched, a subsequent matching failure cannot
1730    cause backtracking into the middle of the group.
1731  .  .
1732  .  .
1733  .\" HTML <a name="bigassertions"></a>  .\" HTML <a name="bigassertions"></a>
# Line 1636  lookbehind assertion is needed to achiev Line 1781  lookbehind assertion is needed to achiev
1781  If you want to force a matching failure at some point in a pattern, the most  If you want to force a matching failure at some point in a pattern, the most
1782  convenient way to do it is with (?!) because an empty string always matches, so  convenient way to do it is with (?!) because an empty string always matches, so
1783  an assertion that requires there not to be an empty string must always fail.  an assertion that requires there not to be an empty string must always fail.
1784    The Perl 5.10 backtracking control verb (*FAIL) or (*F) is essentially a
1785    synonym for (?!).
1786  .  .
1787  .  .
1788  .\" HTML <a name="lookbehind"></a>  .\" HTML <a name="lookbehind"></a>
# Line 1660  is permitted, but Line 1807  is permitted, but
1807  .sp  .sp
1808  causes an error at compile time. Branches that match different length strings  causes an error at compile time. Branches that match different length strings
1809  are permitted only at the top level of a lookbehind assertion. This is an  are permitted only at the top level of a lookbehind assertion. This is an
1810  extension compared with Perl (at least for 5.8), which requires all branches to  extension compared with Perl (5.8 and 5.10), which requires all branches to
1811  match the same length of string. An assertion such as  match the same length of string. An assertion such as
1812  .sp  .sp
1813    (?<=ab(c|de))    (?<=ab(c|de))
1814  .sp  .sp
1815  is not permitted, because its single top-level branch can match two different  is not permitted, because its single top-level branch can match two different
1816  lengths, but it is acceptable if rewritten to use two top-level branches:  lengths, but it is acceptable to PCRE if rewritten to use two top-level
1817    branches:
1818  .sp  .sp
1819    (?<=abc|abde)    (?<=abc|abde)
1820  .sp  .sp
# Line 1675  In some cases, the Perl 5.10 escape sequ Line 1823  In some cases, the Perl 5.10 escape sequ
1823  .\" </a>  .\" </a>
1824  (see above)  (see above)
1825  .\"  .\"
1826  can be used instead of a lookbehind assertion; this is not restricted to a  can be used instead of a lookbehind assertion to get round the fixed-length
1827  fixed-length.  restriction.
1828  .P  .P
1829  The implementation of lookbehind assertions is, for each alternative, to  The implementation of lookbehind assertions is, for each alternative, to
1830  temporarily move the current position back by the fixed length and then try to  temporarily move the current position back by the fixed length and then try to
# Line 1688  to appear in lookbehind assertions, beca Line 1836  to appear in lookbehind assertions, beca
1836  the length of the lookbehind. The \eX and \eR escapes, which can match  the length of the lookbehind. The \eX and \eR escapes, which can match
1837  different numbers of bytes, are also not permitted.  different numbers of bytes, are also not permitted.
1838  .P  .P
1839    .\" HTML <a href="#subpatternsassubroutines">
1840    .\" </a>
1841    "Subroutine"
1842    .\"
1843    calls (see below) such as (?2) or (?&X) are permitted in lookbehinds, as long
1844    as the subpattern matches a fixed-length string.
1845    .\" HTML <a href="#recursion">
1846    .\" </a>
1847    Recursion,
1848    .\"
1849    however, is not supported.
1850    .P
1851  Possessive quantifiers can be used in conjunction with lookbehind assertions to  Possessive quantifiers can be used in conjunction with lookbehind assertions to
1852  specify efficient matching at the end of the subject string. Consider a simple  specify efficient matching of fixed-length strings at the end of subject
1853  pattern such as  strings. Consider a simple pattern such as
1854  .sp  .sp
1855    abcd$    abcd$
1856  .sp  .sp
# Line 1754  characters that are not "999". Line 1914  characters that are not "999".
1914  .sp  .sp
1915  It is possible to cause the matching process to obey a subpattern  It is possible to cause the matching process to obey a subpattern
1916  conditionally or to choose between two alternative subpatterns, depending on  conditionally or to choose between two alternative subpatterns, depending on
1917  the result of an assertion, or whether a previous capturing subpattern matched  the result of an assertion, or whether a specific capturing subpattern has
1918  or not. The two possible forms of conditional subpattern are  already been matched. The two possible forms of conditional subpattern are:
1919  .sp  .sp
1920    (?(condition)yes-pattern)    (?(condition)yes-pattern)
1921    (?(condition)yes-pattern|no-pattern)    (?(condition)yes-pattern|no-pattern)
# Line 1771  recursion, a pseudo-condition called DEF Line 1931  recursion, a pseudo-condition called DEF
1931  .rs  .rs
1932  .sp  .sp
1933  If the text between the parentheses consists of a sequence of digits, the  If the text between the parentheses consists of a sequence of digits, the
1934  condition is true if the capturing subpattern of that number has previously  condition is true if a capturing subpattern of that number has previously
1935  matched. An alternative notation is to precede the digits with a plus or minus  matched. If there is more than one capturing subpattern with the same number
1936  sign. In this case, the subpattern number is relative rather than absolute.  (see the earlier
1937  The most recently opened parentheses can be referenced by (?(-1), the next most  .\"
1938  recent by (?(-2), and so on. In looping constructs it can also make sense to  .\" HTML <a href="#recursion">
1939  refer to subsequent groups with constructs such as (?(+2).  .\" </a>
1940    section about duplicate subpattern numbers),
1941    .\"
1942    the condition is true if any of them have been set. An alternative notation is
1943    to precede the digits with a plus or minus sign. In this case, the subpattern
1944    number is relative rather than absolute. The most recently opened parentheses
1945    can be referenced by (?(-1), the next most recent by (?(-2), and so on. In
1946    looping constructs it can also make sense to refer to subsequent groups with
1947    constructs such as (?(+2).
1948  .P  .P
1949  Consider the following pattern, which contains non-significant white space to  Consider the following pattern, which contains non-significant white space to
1950  make it more readable (assume the PCRE_EXTENDED option) and to divide it into  make it more readable (assume the PCRE_EXTENDED option) and to divide it into
# Line 1817  Rewriting the above example to use a nam Line 1985  Rewriting the above example to use a nam
1985  .sp  .sp
1986    (?<OPEN> \e( )?    [^()]+    (?(<OPEN>) \e) )    (?<OPEN> \e( )?    [^()]+    (?(<OPEN>) \e) )
1987  .sp  .sp
1988    If the name used in a condition of this kind is a duplicate, the test is
1989    applied to all subpatterns of the same name, and is true if any one of them has
1990    matched.
1991  .  .
1992  .SS "Checking for pattern recursion"  .SS "Checking for pattern recursion"
1993  .rs  .rs
# Line 1828  letter R, for example: Line 1999  letter R, for example:
1999  .sp  .sp
2000    (?(R3)...) or (?(R&name)...)    (?(R3)...) or (?(R&name)...)
2001  .sp  .sp
2002  the condition is true if the most recent recursion is into the subpattern whose  the condition is true if the most recent recursion is into a subpattern whose
2003  number or name is given. This condition does not check the entire recursion  number or name is given. This condition does not check the entire recursion
2004  stack.  stack. If the name used in a condition of this kind is a duplicate, the test is
2005    applied to all subpatterns of the same name, and is true if any one of them is
2006    the most recent recursion.
2007  .P  .P
2008  At "top level", all these recursion test conditions are false. Recursive  At "top level", all these recursion test conditions are false.
2009  patterns are described below.  .\" HTML <a href="#recursion">
2010    .\" </a>
2011    The syntax for recursive patterns
2012    .\"
2013    is described below.
2014  .  .
2015  .SS "Defining subpatterns for use by reference only"  .SS "Defining subpatterns for use by reference only"
2016  .rs  .rs
# Line 1842  If the condition is the string (DEFINE), Line 2019  If the condition is the string (DEFINE),
2019  name DEFINE, the condition is always false. In this case, there may be only one  name DEFINE, the condition is always false. In this case, there may be only one
2020  alternative in the subpattern. It is always skipped if control reaches this  alternative in the subpattern. It is always skipped if control reaches this
2021  point in the pattern; the idea of DEFINE is that it can be used to define  point in the pattern; the idea of DEFINE is that it can be used to define
2022  "subroutines" that can be referenced from elsewhere. (The use of "subroutines"  "subroutines" that can be referenced from elsewhere. (The use of
2023    .\" HTML <a href="#subpatternsassubroutines">
2024    .\" </a>
2025    "subroutines"
2026    .\"
2027  is described below.) For example, a pattern to match an IPv4 address could be  is described below.) For example, a pattern to match an IPv4 address could be
2028  written like this (ignore whitespace and line breaks):  written like this (ignore whitespace and line breaks):
2029  .sp  .sp
# Line 1852  written like this (ignore whitespace and Line 2033  written like this (ignore whitespace and
2033  The first part of the pattern is a DEFINE group inside which a another group  The first part of the pattern is a DEFINE group inside which a another group
2034  named "byte" is defined. This matches an individual component of an IPv4  named "byte" is defined. This matches an individual component of an IPv4
2035  address (a number less than 256). When matching takes place, this part of the  address (a number less than 256). When matching takes place, this part of the
2036  pattern is skipped because DEFINE acts like a false condition.  pattern is skipped because DEFINE acts like a false condition. The rest of the
2037  .P  pattern uses references to the named group to match the four dot-separated
2038  The rest of the pattern uses references to the named group to match the four  components of an IPv4 address, insisting on a word boundary at each end.
 dot-separated components of an IPv4 address, insisting on a word boundary at  
 each end.  
2039  .  .
2040  .SS "Assertion conditions"  .SS "Assertion conditions"
2041  .rs  .rs
# Line 1913  recursively to the pattern in which it a Line 2092  recursively to the pattern in which it a
2092  Obviously, PCRE cannot support the interpolation of Perl code. Instead, it  Obviously, PCRE cannot support the interpolation of Perl code. Instead, it
2093  supports special syntax for recursion of the entire pattern, and also for  supports special syntax for recursion of the entire pattern, and also for
2094  individual subpattern recursion. After its introduction in PCRE and Python,  individual subpattern recursion. After its introduction in PCRE and Python,
2095  this kind of recursion was introduced into Perl at release 5.10.  this kind of recursion was subsequently introduced into Perl at release 5.10.
2096  .P  .P
2097  A special item that consists of (? followed by a number greater than zero and a  A special item that consists of (? followed by a number greater than zero and a
2098  closing parenthesis is a recursive call of the subpattern of the given number,  closing parenthesis is a recursive call of the subpattern of the given number,
2099  provided that it occurs inside that subpattern. (If not, it is a "subroutine"  provided that it occurs inside that subpattern. (If not, it is a
2100    .\" HTML <a href="#subpatternsassubroutines">
2101    .\" </a>
2102    "subroutine"
2103    .\"
2104  call, which is described in the next section.) The special item (?R) or (?0) is  call, which is described in the next section.) The special item (?R) or (?0) is
2105  a recursive call of the entire regular expression.  a recursive call of the entire regular expression.
2106  .P  .P
 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.  
 .P  
2107  This PCRE pattern solves the nested parentheses problem (assume the  This PCRE pattern solves the nested parentheses problem (assume the
2108  PCRE_EXTENDED option is set so that white space is ignored):  PCRE_EXTENDED option is set so that white space is ignored):
2109  .sp  .sp
2110    \e( ( (?>[^()]+) | (?R) )* \e)    \e( ( [^()]++ | (?R) )* \e)
2111  .sp  .sp
2112  First it matches an opening parenthesis. Then it matches any number of  First it matches an opening parenthesis. Then it matches any number of
2113  substrings which can either be a sequence of non-parentheses, or a recursive  substrings which can either be a sequence of non-parentheses, or a recursive
2114  match of the pattern itself (that is, a correctly parenthesized substring).  match of the pattern itself (that is, a correctly parenthesized substring).
2115  Finally there is a closing parenthesis.  Finally there is a closing parenthesis. Note the use of a possessive quantifier
2116    to avoid backtracking into sequences of non-parentheses.
2117  .P  .P
2118  If this were part of a larger pattern, you would not want to recurse the entire  If this were part of a larger pattern, you would not want to recurse the entire
2119  pattern, so instead you could use this:  pattern, so instead you could use this:
2120  .sp  .sp
2121    ( \e( ( (?>[^()]+) | (?1) )* \e) )    ( \e( ( [^()]++ | (?1) )* \e) )
2122  .sp  .sp
2123  We have put the pattern into parentheses, and caused the recursion to refer to  We have put the pattern into parentheses, and caused the recursion to refer to
2124  them instead of the whole pattern.  them instead of the whole pattern.
2125  .P  .P
2126  In a larger pattern, keeping track of parenthesis numbers can be tricky. This  In a larger pattern, keeping track of parenthesis numbers can be tricky. This
2127  is made easier by the use of relative references. (A Perl 5.10 feature.)  is made easier by the use of relative references (a Perl 5.10 feature).
2128  Instead of (?1) in the pattern above you can write (?-2) to refer to the second  Instead of (?1) in the pattern above you can write (?-2) to refer to the second
2129  most recently opened parentheses preceding the recursion. In other words, a  most recently opened parentheses preceding the recursion. In other words, a
2130  negative number counts capturing parentheses leftwards from the point at which  negative number counts capturing parentheses leftwards from the point at which
# Line 1954  it is encountered. Line 2133  it is encountered.
2133  It is also possible to refer to subsequently opened parentheses, by writing  It is also possible to refer to subsequently opened parentheses, by writing
2134  references such as (?+2). However, these cannot be recursive because the  references such as (?+2). However, these cannot be recursive because the
2135  reference is not inside the parentheses that are referenced. They are always  reference is not inside the parentheses that are referenced. They are always
2136  "subroutine" calls, as described in the next section.  .\" HTML <a href="#subpatternsassubroutines">
2137    .\" </a>
2138    "subroutine"
2139    .\"
2140    calls, as described in the next section.
2141  .P  .P
2142  An alternative approach is to use named parentheses instead. The Perl syntax  An alternative approach is to use named parentheses instead. The Perl syntax
2143  for this is (?&name); PCRE's earlier syntax (?P>name) is also supported. We  for this is (?&name); PCRE's earlier syntax (?P>name) is also supported. We
2144  could rewrite the above example as follows:  could rewrite the above example as follows:
2145  .sp  .sp
2146    (?<pn> \e( ( (?>[^()]+) | (?&pn) )* \e) )    (?<pn> \e( ( [^()]++ | (?&pn) )* \e) )
2147  .sp  .sp
2148  If there is more than one subpattern with the same name, the earliest one is  If there is more than one subpattern with the same name, the earliest one is
2149  used.  used.
2150  .P  .P
2151  This particular example pattern that we have been looking at contains nested  This particular example pattern that we have been looking at contains nested
2152  unlimited repeats, and so the use of atomic grouping for matching strings of  unlimited repeats, and so the use of a possessive quantifier for matching
2153  non-parentheses is important when applying the pattern to strings that do not  strings of non-parentheses is important when applying the pattern to strings
2154  match. For example, when this pattern is applied to  that do not match. For example, when this pattern is applied to
2155  .sp  .sp
2156    (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()    (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
2157  .sp  .sp
2158  it yields "no match" quickly. However, if atomic grouping is not used,  it yields "no match" quickly. However, if a possessive quantifier is not used,
2159  the match runs for a very long time indeed because there are so many different  the match runs for a very long time indeed because there are so many different
2160  ways the + and * repeats can carve up the subject, and all have to be tested  ways the + and * repeats can carve up the subject, and all have to be tested
2161  before failure can be reported.  before failure can be reported.
2162  .P  .P
2163  At the end of a match, the values set for any capturing subpatterns are those  At the end of a match, the values of capturing parentheses are those from
2164  from the outermost level of the recursion at which the subpattern value is set.  the outermost level. If you want to obtain intermediate values, a callout
2165  If you want to obtain intermediate values, a callout function can be used (see  function can be used (see below and the
 below and the  
2166  .\" HREF  .\" HREF
2167  \fBpcrecallout\fP  \fBpcrecallout\fP
2168  .\"  .\"
# Line 1988  documentation). If the pattern above is Line 2170  documentation). If the pattern above is
2170  .sp  .sp
2171    (ab(cd)ef)    (ab(cd)ef)
2172  .sp  .sp
2173  the value for the capturing parentheses is "ef", which is the last value taken  the value for the inner capturing parentheses (numbered 2) is "ef", which is
2174  on at the top level. If additional parentheses are added, giving  the last value taken on at the top level. If a capturing subpattern is not
2175  .sp  matched at the top level, its final value is unset, even if it is (temporarily)
2176    \e( ( ( (?>[^()]+) | (?R) )* ) \e)  set at a deeper level.
2177       ^                        ^  .P
2178       ^                        ^  If there are more than 15 capturing parentheses in a pattern, PCRE has to
2179  .sp  obtain extra memory to store data during a recursion, which it does by using
2180  the string they capture is "ab(cd)ef", the contents of the top level  \fBpcre_malloc\fP, freeing it via \fBpcre_free\fP afterwards. If no memory can
2181  parentheses. If there are more than 15 capturing parentheses in a pattern, PCRE  be obtained, the match fails with the PCRE_ERROR_NOMEMORY error.
 has to obtain extra memory to store data during a recursion, which it does by  
 using \fBpcre_malloc\fP, freeing it via \fBpcre_free\fP afterwards. If no  
 memory can be obtained, the match fails with the PCRE_ERROR_NOMEMORY error.  
2182  .P  .P
2183  Do not confuse the (?R) item with the condition (R), which tests for recursion.  Do not confuse the (?R) item with the condition (R), which tests for recursion.
2184  Consider this pattern, which matches text in angle brackets, allowing for  Consider this pattern, which matches text in angle brackets, allowing for
# Line 2013  different alternatives for the recursive Line 2192  different alternatives for the recursive
2192  is the actual recursive call.  is the actual recursive call.
2193  .  .
2194  .  .
2195    .\" HTML <a name="recursiondifference"></a>
2196    .SS "Recursion difference from Perl"
2197    .rs
2198    .sp
2199    In PCRE (like Python, but unlike Perl), a recursive subpattern call is always
2200    treated as an atomic group. That is, once it has matched some of the subject
2201    string, it is never re-entered, even if it contains untried alternatives and
2202    there is a subsequent matching failure. This can be illustrated by the
2203    following pattern, which purports to match a palindromic string that contains
2204    an odd number of characters (for example, "a", "aba", "abcba", "abcdcba"):
2205    .sp
2206      ^(.|(.)(?1)\e2)$
2207    .sp
2208    The idea is that it either matches a single character, or two identical
2209    characters surrounding a sub-palindrome. In Perl, this pattern works; in PCRE
2210    it does not if the pattern is longer than three characters. Consider the
2211    subject string "abcba":
2212    .P
2213    At the top level, the first character is matched, but as it is not at the end
2214    of the string, the first alternative fails; the second alternative is taken
2215    and the recursion kicks in. The recursive call to subpattern 1 successfully
2216    matches the next character ("b"). (Note that the beginning and end of line
2217    tests are not part of the recursion).
2218    .P
2219    Back at the top level, the next character ("c") is compared with what
2220    subpattern 2 matched, which was "a". This fails. Because the recursion is
2221    treated as an atomic group, there are now no backtracking points, and so the
2222    entire match fails. (Perl is able, at this point, to re-enter the recursion and
2223    try the second alternative.) However, if the pattern is written with the
2224    alternatives in the other order, things are different:
2225    .sp
2226      ^((.)(?1)\e2|.)$
2227    .sp
2228    This time, the recursing alternative is tried first, and continues to recurse
2229    until it runs out of characters, at which point the recursion fails. But this
2230    time we do have another alternative to try at the higher level. That is the big
2231    difference: in the previous case the remaining alternative is at a deeper
2232    recursion level, which PCRE cannot use.
2233    .P
2234    To change the pattern so that matches all palindromic strings, not just those
2235    with an odd number of characters, it is tempting to change the pattern to this:
2236    .sp
2237      ^((.)(?1)\e2|.?)$
2238    .sp
2239    Again, this works in Perl, but not in PCRE, and for the same reason. When a
2240    deeper recursion has matched a single character, it cannot be entered again in
2241    order to match an empty string. The solution is to separate the two cases, and
2242    write out the odd and even cases as alternatives at the higher level:
2243    .sp
2244      ^(?:((.)(?1)\e2|)|((.)(?3)\e4|.))
2245    .sp
2246    If you want to match typical palindromic phrases, the pattern has to ignore all
2247    non-word characters, which can be done like this:
2248    .sp
2249      ^\eW*+(?:((.)\eW*+(?1)\eW*+\e2|)|((.)\eW*+(?3)\eW*+\e4|\eW*+.\eW*+))\eW*+$
2250    .sp
2251    If run with the PCRE_CASELESS option, this pattern matches phrases such as "A
2252    man, a plan, a canal: Panama!" and it works well in both PCRE and Perl. Note
2253    the use of the possessive quantifier *+ to avoid backtracking into sequences of
2254    non-word characters. Without this, PCRE takes a great deal longer (ten times or
2255    more) to match typical phrases, and Perl takes so long that you think it has
2256    gone into a loop.
2257    .P
2258    \fBWARNING\fP: The palindrome-matching patterns above work only if the subject
2259    string does not start with a palindrome that is shorter than the entire string.
2260    For example, although "abcba" is correctly matched, if the subject is "ababa",
2261    PCRE finds the palindrome "aba" at the start, then fails at top level because
2262    the end of the string does not follow. Once again, it cannot jump back into the
2263    recursion to try other alternatives, so the entire match fails.
2264    .
2265    .
2266  .\" HTML <a name="subpatternsassubroutines"></a>  .\" HTML <a name="subpatternsassubroutines"></a>
2267  .SH "SUBPATTERNS AS SUBROUTINES"  .SH "SUBPATTERNS AS SUBROUTINES"
2268  .rs  .rs
# Line 2039  matches "sense and sensibility" and "res Line 2289  matches "sense and sensibility" and "res
2289  is used, it does match "sense and responsibility" as well as the other two  is used, it does match "sense and responsibility" as well as the other two
2290  strings. Another example is given in the discussion of DEFINE above.  strings. Another example is given in the discussion of DEFINE above.
2291  .P  .P
2292  Like recursive subpatterns, a "subroutine" call is always treated as an atomic  Like recursive subpatterns, a subroutine call is always treated as an atomic
2293  group. That is, once it has matched some of the subject string, it is never  group. That is, once it has matched some of the subject string, it is never
2294  re-entered, even if it contains untried alternatives and there is a subsequent  re-entered, even if it contains untried alternatives and there is a subsequent
2295  matching failure.  matching failure. Any capturing parentheses that are set during the subroutine
2296    call revert to their previous values afterwards.
2297  .P  .P
2298  When a subpattern is used as a subroutine, processing options such as  When a subpattern is used as a subroutine, processing options such as
2299  case-independence are fixed when the subpattern is defined. They cannot be  case-independence are fixed when the subpattern is defined. They cannot be
# Line 2111  description of the interface to the call Line 2362  description of the interface to the call
2362  documentation.  documentation.
2363  .  .
2364  .  .
2365    .\" HTML <a name="backtrackcontrol"></a>
2366  .SH "BACKTRACKING CONTROL"  .SH "BACKTRACKING CONTROL"
2367  .rs  .rs
2368  .sp  .sp
# Line 2126  a backtracking algorithm. With the excep Line 2378  a backtracking algorithm. With the excep
2378  failing negative assertion, they cause an error if encountered by  failing negative assertion, they cause an error if encountered by
2379  \fBpcre_dfa_exec()\fP.  \fBpcre_dfa_exec()\fP.
2380  .P  .P
2381    If any of these verbs are used in an assertion or subroutine subpattern
2382    (including recursive subpatterns), their effect is confined to that subpattern;
2383    it does not extend to the surrounding pattern. Note that such subpatterns are
2384    processed as anchored at the point where they are tested.
2385    .P
2386  The new verbs make use of what was previously invalid syntax: an opening  The new verbs make use of what was previously invalid syntax: an opening
2387  parenthesis followed by an asterisk. In Perl, they are generally of the form  parenthesis followed by an asterisk. They are generally of the form
2388  (*VERB:ARG) but PCRE does not support the use of arguments, so its general  (*VERB) or (*VERB:NAME). Some may take either form, with differing behaviour,
2389  form is just (*VERB). Any number of these verbs may occur in a pattern. There  depending on whether or not an argument is present. An name is a sequence of
2390  are two kinds:  letters, digits, and underscores. If the name is empty, that is, if the closing
2391    parenthesis immediately follows the colon, the effect is as if the colon were
2392    not there. Any number of these verbs may occur in a pattern.
2393    .P
2394    PCRE contains some optimizations that are used to speed up matching by running
2395    some checks at the start of each match attempt. For example, it may know the
2396    minimum length of matching subject, or that a particular character must be
2397    present. When one of these optimizations suppresses the running of a match, any
2398    included backtracking verbs will not, of course, be processed. You can suppress
2399    the start-of-match optimizations by setting the PCRE_NO_START_OPTIMIZE option
2400    when calling \fBpcre_exec()\fP.
2401    .
2402  .  .
2403  .SS "Verbs that act immediately"  .SS "Verbs that act immediately"
2404  .rs  .rs
2405  .sp  .sp
2406  The following verbs act as soon as they are encountered:  The following verbs act as soon as they are encountered. They may not be
2407    followed by a name.
2408  .sp  .sp
2409     (*ACCEPT)     (*ACCEPT)
2410  .sp  .sp
2411  This verb causes the match to end successfully, skipping the remainder of the  This verb causes the match to end successfully, skipping the remainder of the
2412  pattern. When inside a recursion, only the innermost pattern is ended  pattern. When inside a recursion, only the innermost pattern is ended
2413  immediately. PCRE differs from Perl in what happens if the (*ACCEPT) is inside  immediately. If (*ACCEPT) is inside capturing parentheses, the data so far is
2414  capturing parentheses. In Perl, the data so far is captured: in PCRE no data is  captured. (This feature was added to PCRE at release 8.00.) For example:
 captured. For example:  
2415  .sp  .sp
2416    A(A|B(*ACCEPT)|C)D    A((?:A|B(*ACCEPT)|C)D)
2417  .sp  .sp
2418  This matches "AB", "AAD", or "ACD", but when it matches "AB", no data is  This matches "AB", "AAD", or "ACD"; when it matches "AB", "B" is captured by
2419  captured.  the outer parentheses.
2420  .sp  .sp
2421    (*FAIL) or (*F)    (*FAIL) or (*F)
2422  .sp  .sp
# Line 2163  callout feature, as for example in this Line 2431  callout feature, as for example in this
2431  A match with the string "aaaa" always fails, but the callout is taken before  A match with the string "aaaa" always fails, but the callout is taken before
2432  each backtrack happens (in this example, 10 times).  each backtrack happens (in this example, 10 times).
2433  .  .
2434    .
2435    .SS "Recording which path was taken"
2436    .rs
2437    .sp
2438    There is one verb whose main purpose is to track how a match was arrived at,
2439    though it also has a secondary use in conjunction with advancing the match
2440    starting point (see (*SKIP) below).
2441    .sp
2442      (*MARK:NAME) or (*:NAME)
2443    .sp
2444    A name is always required with this verb. There may be as many instances of
2445    (*MARK) as you like in a pattern, and their names do not have to be unique.
2446    .P
2447    When a match succeeds, the name of the last-encountered (*MARK) is passed back
2448    to the caller via the \fIpcre_extra\fP data structure, as described in the
2449    .\" HTML <a href="pcreapi.html#extradata">
2450    .\" </a>
2451    section on \fIpcre_extra\fP
2452    .\"
2453    in the
2454    .\" HREF
2455    \fBpcreapi\fP
2456    .\"
2457    documentation. No data is returned for a partial match. Here is an example of
2458    \fBpcretest\fP output, where the /K modifier requests the retrieval and
2459    outputting of (*MARK) data:
2460    .sp
2461      /X(*MARK:A)Y|X(*MARK:B)Z/K
2462      XY
2463       0: XY
2464      MK: A
2465      XZ
2466       0: XZ
2467      MK: B
2468    .sp
2469    The (*MARK) name is tagged with "MK:" in this output, and in this example it
2470    indicates which of the two alternatives matched. This is a more efficient way
2471    of obtaining this information than putting each alternative in its own
2472    capturing parentheses.
2473    .P
2474    A name may also be returned after a failed match if the final path through the
2475    pattern involves (*MARK). However, unless (*MARK) used in conjunction with
2476    (*COMMIT), this is unlikely to happen for an unanchored pattern because, as the
2477    starting point for matching is advanced, the final check is often with an empty
2478    string, causing a failure before (*MARK) is reached. For example:
2479    .sp
2480      /X(*MARK:A)Y|X(*MARK:B)Z/K
2481      XP
2482      No match
2483    .sp
2484    There are three potential starting points for this match (starting with X,
2485    starting with P, and with an empty string). If the pattern is anchored, the
2486    result is different:
2487    .sp
2488      /^X(*MARK:A)Y|^X(*MARK:B)Z/K
2489      XP
2490      No match, mark = B
2491    .sp
2492    PCRE's start-of-match optimizations can also interfere with this. For example,
2493    if, as a result of a call to \fBpcre_study()\fP, it knows the minimum
2494    subject length for a match, a shorter subject will not be scanned at all.
2495    .P
2496    Note that similar anomalies (though different in detail) exist in Perl, no
2497    doubt for the same reasons. The use of (*MARK) data after a failed match of an
2498    unanchored pattern is not recommended, unless (*COMMIT) is involved.
2499    .
2500    .
2501  .SS "Verbs that act after backtracking"  .SS "Verbs that act after backtracking"
2502  .rs  .rs
2503  .sp  .sp
2504  The following verbs do nothing when they are encountered. Matching continues  The following verbs do nothing when they are encountered. Matching continues
2505  with what follows, but if there is no subsequent match, a failure is forced.  with what follows, but if there is no subsequent match, causing a backtrack to
2506  The verbs differ in exactly what kind of failure occurs.  the verb, a failure is forced. That is, backtracking cannot pass to the left of
2507    the verb. However, when one of these verbs appears inside an atomic group, its
2508    effect is confined to that group, because once the group has been matched,
2509    there is never any backtracking into it. In this situation, backtracking can
2510    "jump back" to the left of the entire atomic group. (Remember also, as stated
2511    above, that this localization also applies in subroutine calls and assertions.)
2512    .P
2513    These verbs differ in exactly what kind of failure occurs when backtracking
2514    reaches them.
2515  .sp  .sp
2516    (*COMMIT)    (*COMMIT)
2517  .sp  .sp
2518  This verb causes the whole match to fail outright if the rest of the pattern  This verb, which may not be followed by a name, causes the whole match to fail
2519  does not match. Even if the pattern is unanchored, no further attempts to find  outright if the rest of the pattern does not match. Even if the pattern is
2520  a match by advancing the start point take place. Once (*COMMIT) has been  unanchored, no further attempts to find a match by advancing the starting point
2521  passed, \fBpcre_exec()\fP is committed to finding a match at the current  take place. Once (*COMMIT) has been passed, \fBpcre_exec()\fP is committed to
2522  starting point, or not at all. For example:  finding a match at the current starting point, or not at all. For example:
2523  .sp  .sp
2524    a+(*COMMIT)b    a+(*COMMIT)b
2525  .sp  .sp
2526  This matches "xxaab" but not "aacaab". It can be thought of as a kind of  This matches "xxaab" but not "aacaab". It can be thought of as a kind of
2527  dynamic anchor, or "I've started, so I must finish."  dynamic anchor, or "I've started, so I must finish." The name of the most
2528  .sp  recently passed (*MARK) in the path is passed back when (*COMMIT) forces a
2529    (*PRUNE)  match failure.
2530  .sp  .P
2531  This verb causes the match to fail at the current position if the rest of the  Note that (*COMMIT) at the start of a pattern is not the same as an anchor,
2532  pattern does not match. If the pattern is unanchored, the normal "bumpalong"  unless PCRE's start-of-match optimizations are turned off, as shown in this
2533  advance to the next starting character then happens. Backtracking can occur as  \fBpcretest\fP example:
2534  usual to the left of (*PRUNE), or when matching to the right of (*PRUNE), but  .sp
2535  if there is no match to the right, backtracking cannot cross (*PRUNE).    /(*COMMIT)abc/
2536  In simple cases, the use of (*PRUNE) is just an alternative to an atomic    xyzabc
2537  group or possessive quantifier, but there are some uses of (*PRUNE) that cannot     0: abc
2538  be expressed in any other way.    xyzabc\eY
2539      No match
2540    .sp
2541    PCRE knows that any match must start with "a", so the optimization skips along
2542    the subject to "a" before running the first match attempt, which succeeds. When
2543    the optimization is disabled by the \eY escape in the second subject, the match
2544    starts at "x" and so the (*COMMIT) causes it to fail without trying any other
2545    starting points.
2546    .sp
2547      (*PRUNE) or (*PRUNE:NAME)
2548    .sp
2549    This verb causes the match to fail at the current starting position in the
2550    subject if the rest of the pattern does not match. If the pattern is
2551    unanchored, the normal "bumpalong" advance to the next starting character then
2552    happens. Backtracking can occur as usual to the left of (*PRUNE), before it is
2553    reached, or when matching to the right of (*PRUNE), but if there is no match to
2554    the right, backtracking cannot cross (*PRUNE). In simple cases, the use of
2555    (*PRUNE) is just an alternative to an atomic group or possessive quantifier,
2556    but there are some uses of (*PRUNE) that cannot be expressed in any other way.
2557    The behaviour of (*PRUNE:NAME) is the same as (*MARK:NAME)(*PRUNE) when the
2558    match fails completely; the name is passed back if this is the final attempt.
2559    (*PRUNE:NAME) does not pass back a name if the match succeeds. In an anchored
2560    pattern (*PRUNE) has the same effect as (*COMMIT).
2561  .sp  .sp
2562    (*SKIP)    (*SKIP)
2563  .sp  .sp
2564  This verb is like (*PRUNE), except that if the pattern is unanchored, the  This verb, when given without a name, is like (*PRUNE), except that if the
2565  "bumpalong" advance is not to the next character, but to the position in the  pattern is unanchored, the "bumpalong" advance is not to the next character,
2566  subject where (*SKIP) was encountered. (*SKIP) signifies that whatever text  but to the position in the subject where (*SKIP) was encountered. (*SKIP)
2567  was matched leading up to it cannot be part of a successful match. Consider:  signifies that whatever text was matched leading up to it cannot be part of a
2568    successful match. Consider:
2569  .sp  .sp
2570    a+(*SKIP)b    a+(*SKIP)b
2571  .sp  .sp
2572  If the subject is "aaaac...", after the first match attempt fails (starting at  If the subject is "aaaac...", after the first match attempt fails (starting at
2573  the first character in the string), the starting point skips on to start the  the first character in the string), the starting point skips on to start the
2574  next attempt at "c". Note that a possessive quantifer does not have the same  next attempt at "c". Note that a possessive quantifer does not have the same
2575  effect in this example; although it would suppress backtracking during the  effect as this example; although it would suppress backtracking during the
2576  first match attempt, the second attempt would start at the second character  first match attempt, the second attempt would start at the second character
2577  instead of skipping on to "c".  instead of skipping on to "c".
2578  .sp  .sp
2579    (*THEN)    (*SKIP:NAME)
2580    .sp
2581    When (*SKIP) has an associated name, its behaviour is modified. If the
2582    following pattern fails to match, the previous path through the pattern is
2583    searched for the most recent (*MARK) that has the same name. If one is found,
2584    the "bumpalong" advance is to the subject position that corresponds to that
2585    (*MARK) instead of to where (*SKIP) was encountered. If no (*MARK) with a
2586    matching name is found, normal "bumpalong" of one character happens (the
2587    (*SKIP) is ignored).
2588    .sp
2589      (*THEN) or (*THEN:NAME)
2590  .sp  .sp
2591  This verb causes a skip to the next alternation if the rest of the pattern does  This verb causes a skip to the next alternation if the rest of the pattern does
2592  not match. That is, it cancels pending backtracking, but only within the  not match. That is, it cancels pending backtracking, but only within the
# Line 2221  for a pattern-based if-then-else block: Line 2597  for a pattern-based if-then-else block:
2597  .sp  .sp
2598  If the COND1 pattern matches, FOO is tried (and possibly further items after  If the COND1 pattern matches, FOO is tried (and possibly further items after
2599  the end of the group if FOO succeeds); on failure the matcher skips to the  the end of the group if FOO succeeds); on failure the matcher skips to the
2600  second alternative and tries COND2, without backtracking into COND1. If (*THEN)  second alternative and tries COND2, without backtracking into COND1. The
2601  is used outside of any alternation, it acts exactly like (*PRUNE).  behaviour of (*THEN:NAME) is exactly the same as (*MARK:NAME)(*THEN) if the
2602    overall match fails. If (*THEN) is not directly inside an alternation, it acts
2603    like (*PRUNE).
2604  .  .
2605  .  .
2606  .SH "SEE ALSO"  .SH "SEE ALSO"
2607  .rs  .rs
2608  .sp  .sp
2609  \fBpcreapi\fP(3), \fBpcrecallout\fP(3), \fBpcrematching\fP(3), \fBpcre\fP(3).  \fBpcreapi\fP(3), \fBpcrecallout\fP(3), \fBpcrematching\fP(3),
2610    \fBpcresyntax\fP(3), \fBpcre\fP(3).
2611  .  .
2612  .  .
2613  .SH AUTHOR  .SH AUTHOR
# Line 2245  Cambridge CB2 3QH, England. Line 2624  Cambridge CB2 3QH, England.
2624  .rs  .rs
2625  .sp  .sp
2626  .nf  .nf
2627  Last updated: 18 March 2009  Last updated: 05 May 2010
2628  Copyright (c) 1997-2009 University of Cambridge.  Copyright (c) 1997-2010 University of Cambridge.
2629  .fi  .fi

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