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1  ChangeLog for PCRE  ChangeLog for PCRE
2  ------------------  ------------------
4  Version 8.00 ??-???-??  Version 8.11 10-Oct-2010
5    ------------------------
7    1.  (*THEN) was not working properly if there were untried alternatives prior
8        to it in the current branch. For example, in ((a|b)(*THEN)(*F)|c..) it
9        backtracked to try for "b" instead of moving to the next alternative branch
10        at the same level (in this case, to look for "c"). The Perl documentation
11        is clear that when (*THEN) is backtracked onto, it goes to the "next
12        alternative in the innermost enclosing group".
14    2.  (*COMMIT) was not overriding (*THEN), as it does in Perl. In a pattern
15        such as   (A(*COMMIT)B(*THEN)C|D)  any failure after matching A should
16        result in overall failure. Similarly, (*COMMIT) now overrides (*PRUNE) and
17        (*SKIP), (*SKIP) overrides (*PRUNE) and (*THEN), and (*PRUNE) overrides
18        (*THEN).
20    3.  If \s appeared in a character class, it removed the VT character from
21        the class, even if it had been included by some previous item, for example
22        in [\x00-\xff\s]. (This was a bug related to the fact that VT is not part
23        of \s, but is part of the POSIX "space" class.)
25    4.  A partial match never returns an empty string (because you can always
26        match an empty string at the end of the subject); however the checking for
27        an empty string was starting at the "start of match" point. This has been
28        changed to the "earliest inspected character" point, because the returned
29        data for a partial match starts at this character. This means that, for
30        example, /(?<=abc)def/ gives a partial match for the subject "abc"
31        (previously it gave "no match").
33    5.  Changes have been made to the way PCRE_PARTIAL_HARD affects the matching
34        of $, \z, \Z, \b, and \B. If the match point is at the end of the string,
35        previously a full match would be given. However, setting PCRE_PARTIAL_HARD
36        has an implication that the given string is incomplete (because a partial
37        match is preferred over a full match). For this reason, these items now
38        give a partial match in this situation. [Aside: previously, the one case
39        /t\b/ matched against "cat" with PCRE_PARTIAL_HARD set did return a partial
40        match rather than a full match, which was wrong by the old rules, but is
41        now correct.]
43    6.  There was a bug in the handling of #-introduced comments, recognized when
44        PCRE_EXTENDED is set, when PCRE_NEWLINE_ANY and PCRE_UTF8 were also set.
45        If a UTF-8 multi-byte character included the byte 0x85 (e.g. +U0445, whose
46        UTF-8 encoding is 0xd1,0x85), this was misinterpreted as a newline when
47        scanning for the end of the comment. (*Character* 0x85 is an "any" newline,
48        but *byte* 0x85 is not, in UTF-8 mode). This bug was present in several
49        places in pcre_compile().
51    7.  Related to (6) above, when pcre_compile() was skipping #-introduced
52        comments when looking ahead for named forward references to subpatterns,
53        the only newline sequence it recognized was NL. It now handles newlines
54        according to the set newline convention.
57    Version 8.10 25-Jun-2010
58    ------------------------
60    1.  Added support for (*MARK:ARG) and for ARG additions to PRUNE, SKIP, and
61        THEN.
63    2.  (*ACCEPT) was not working when inside an atomic group.
65    3.  Inside a character class, \B is treated as a literal by default, but
66        faulted if PCRE_EXTRA is set. This mimics Perl's behaviour (the -w option
67        causes the error). The code is unchanged, but I tidied the documentation.
69    4.  Inside a character class, PCRE always treated \R and \X as literals,
70        whereas Perl faults them if its -w option is set. I have changed PCRE so
71        that it faults them when PCRE_EXTRA is set.
73    5.  Added support for \N, which always matches any character other than
74        newline. (It is the same as "." when PCRE_DOTALL is not set.)
76    6.  When compiling pcregrep with newer versions of gcc which may have
77        FORTIFY_SOURCE set, several warnings "ignoring return value of 'fwrite',
78        declared with attribute warn_unused_result" were given. Just casting the
79        result to (void) does not stop the warnings; a more elaborate fudge is
80        needed. I've used a macro to implement this.
82    7.  Minor change to pcretest.c to avoid a compiler warning.
84    8.  Added four artifical Unicode properties to help with an option to make
85        \s etc use properties (see next item). The new properties are: Xan
86        (alphanumeric), Xsp (Perl space), Xps (POSIX space), and Xwd (word).
88    9.  Added PCRE_UCP to make \b, \d, \s, \w, and certain POSIX character classes
89        use Unicode properties. (*UCP) at the start of a pattern can be used to set
90        this option. Modified pcretest to add /W to test this facility. Added
91        REG_UCP to make it available via the POSIX interface.
93    10. Added --line-buffered to pcregrep.
95    11. In UTF-8 mode, if a pattern that was compiled with PCRE_CASELESS was
96        studied, and the match started with a letter with a code point greater than
97        127 whose first byte was different to the first byte of the other case of
98        the letter, the other case of this starting letter was not recognized
99        (#976).
101    12. If a pattern that was studied started with a repeated Unicode property
102        test, for example, \p{Nd}+, there was the theoretical possibility of
103        setting up an incorrect bitmap of starting bytes, but fortunately it could
104        not have actually happened in practice until change 8 above was made (it
105        added property types that matched character-matching opcodes).
107    13. pcre_study() now recognizes \h, \v, and \R when constructing a bit map of
108        possible starting bytes for non-anchored patterns.
110    14. Extended the "auto-possessify" feature of pcre_compile(). It now recognizes
111        \R, and also a number of cases that involve Unicode properties, both
112        explicit and implicit when PCRE_UCP is set.
114    15. If a repeated Unicode property match (e.g. \p{Lu}*) was used with non-UTF-8
115        input, it could crash or give wrong results if characters with values
116        greater than 0xc0 were present in the subject string. (Detail: it assumed
117        UTF-8 input when processing these items.)
119    16. Added a lot of (int) casts to avoid compiler warnings in systems where
120        size_t is 64-bit (#991).
122    17. Added a check for running out of memory when PCRE is compiled with
123        --disable-stack-for-recursion (#990).
125    18. If the last data line in a file for pcretest does not have a newline on
126        the end, a newline was missing in the output.
128    19. The default pcre_chartables.c file recognizes only ASCII characters (values
129        less than 128) in its various bitmaps. However, there is a facility for
130        generating tables according to the current locale when PCRE is compiled. It
131        turns out that in some environments, 0x85 and 0xa0, which are Unicode space
132        characters, are recognized by isspace() and therefore were getting set in
133        these tables, and indeed these tables seem to approximate to ISO 8859. This
134        caused a problem in UTF-8 mode when pcre_study() was used to create a list
135        of bytes that can start a match. For \s, it was including 0x85 and 0xa0,
136        which of course cannot start UTF-8 characters. I have changed the code so
137        that only real ASCII characters (less than 128) and the correct starting
138        bytes for UTF-8 encodings are set for characters greater than 127 when in
139        UTF-8 mode. (When PCRE_UCP is set - see 9 above - the code is different
140        altogether.)
142    20. Added the /T option to pcretest so as to be able to run tests with non-
143        standard character tables, thus making it possible to include the tests
144        used for 19 above in the standard set of tests.
146    21. A pattern such as (?&t)(?#()(?(DEFINE)(?<t>a)) which has a forward
147        reference to a subpattern the other side of a comment that contains an
148        opening parenthesis caused either an internal compiling error, or a
149        reference to the wrong subpattern.
152    Version 8.02 19-Mar-2010
153    ------------------------
155    1.  The Unicode data tables have been updated to Unicode 5.2.0.
157    2.  Added the option --libs-cpp to pcre-config, but only when C++ support is
158        configured.
160    3.  Updated the licensing terms in the pcregexp.pas file, as agreed with the
161        original author of that file, following a query about its status.
163    4.  On systems that do not have stdint.h (e.g. Solaris), check for and include
164        inttypes.h instead. This fixes a bug that was introduced by change 8.01/8.
166    5.  A pattern such as (?&t)*+(?(DEFINE)(?<t>.)) which has a possessive
167        quantifier applied to a forward-referencing subroutine call, could compile
168        incorrect code or give the error "internal error: previously-checked
169        referenced subpattern not found".
171    6.  Both MS Visual Studio and Symbian OS have problems with initializing
172        variables to point to external functions. For these systems, therefore,
173        pcre_malloc etc. are now initialized to local functions that call the
174        relevant global functions.
176    7.  There were two entries missing in the vectors called coptable and poptable
177        in pcre_dfa_exec.c. This could lead to memory accesses outsize the vectors.
178        I've fixed the data, and added a kludgy way of testing at compile time that
179        the lengths are correct (equal to the number of opcodes).
181    8.  Following on from 7, I added a similar kludge to check the length of the
182        eint vector in pcreposix.c.
184    9.  Error texts for pcre_compile() are held as one long string to avoid too
185        much relocation at load time. To find a text, the string is searched,
186        counting zeros. There was no check for running off the end of the string,
187        which could happen if a new error number was added without updating the
188        string.
190    10. \K gave a compile-time error if it appeared in a lookbehind assersion.
192    11. \K was not working if it appeared in an atomic group or in a group that
193        was called as a "subroutine", or in an assertion. Perl 5.11 documents that
194        \K is "not well defined" if used in an assertion. PCRE now accepts it if
195        the assertion is positive, but not if it is negative.
197    12. Change 11 fortuitously reduced the size of the stack frame used in the
198        "match()" function of pcre_exec.c by one pointer. Forthcoming
199        implementation of support for (*MARK) will need an extra pointer on the
200        stack; I have reserved it now, so that the stack frame size does not
201        decrease.
203    13. A pattern such as (?P<L1>(?P<L2>0)|(?P>L2)(?P>L1)) in which the only other
204        item in branch that calls a recursion is a subroutine call - as in the
205        second branch in the above example - was incorrectly given the compile-
206        time error "recursive call could loop indefinitely" because pcre_compile()
207        was not correctly checking the subroutine for matching a non-empty string.
209    14. The checks for overrunning compiling workspace could trigger after an
210        overrun had occurred. This is a "should never occur" error, but it can be
211        triggered by pathological patterns such as hundreds of nested parentheses.
212        The checks now trigger 100 bytes before the end of the workspace.
214    15. Fix typo in configure.ac: "srtoq" should be "strtoq".
217    Version 8.01 19-Jan-2010
218    ------------------------
220    1.  If a pattern contained a conditional subpattern with only one branch (in
221        particular, this includes all (*DEFINE) patterns), a call to pcre_study()
222        computed the wrong minimum data length (which is of course zero for such
223        subpatterns). This could cause incorrect "no match" results.
225    2.  For patterns such as (?i)a(?-i)b|c where an option setting at the start of
226        the pattern is reset in the first branch, pcre_compile() failed with
227        "internal error: code overflow at offset...". This happened only when
228        the reset was to the original external option setting. (An optimization
229        abstracts leading options settings into an external setting, which was the
230        cause of this.)
232    3.  A pattern such as ^(?!a(*SKIP)b) where a negative assertion contained one
233        of the verbs SKIP, PRUNE, or COMMIT, did not work correctly. When the
234        assertion pattern did not match (meaning that the assertion was true), it
235        was incorrectly treated as false if the SKIP had been reached during the
236        matching. This also applied to assertions used as conditions.
238    4.  If an item that is not supported by pcre_dfa_exec() was encountered in an
239        assertion subpattern, including such a pattern used as a condition,
240        unpredictable results occurred, instead of the error return
243    5.  The C++ GlobalReplace function was not working like Perl for the special
244        situation when an empty string is matched. It now does the fancy magic
245        stuff that is necessary.
247    6.  In pcre_internal.h, obsolete includes to setjmp.h and stdarg.h have been
248        removed. (These were left over from very, very early versions of PCRE.)
250    7.  Some cosmetic changes to the code to make life easier when compiling it
251        as part of something else:
253        (a) Change DEBUG to PCRE_DEBUG.
255        (b) In pcre_compile(), rename the member of the "branch_chain" structure
256            called "current" as "current_branch", to prevent a collision with the
257            Linux macro when compiled as a kernel module.
259        (c) In pcre_study(), rename the function set_bit() as set_table_bit(), to
260            prevent a collision with the Linux macro when compiled as a kernel
261            module.
263    8.  In pcre_compile() there are some checks for integer overflows that used to
264        cast potentially large values to (double). This has been changed to that
265        when building, a check for int64_t is made, and if it is found, it is used
266        instead, thus avoiding the use of floating point arithmetic. (There is no
267        other use of FP in PCRE.) If int64_t is not found, the fallback is to
268        double.
270    9.  Added two casts to avoid signed/unsigned warnings from VS Studio Express
271        2005 (difference between two addresses compared to an unsigned value).
273    10. Change the standard AC_CHECK_LIB test for libbz2 in configure.ac to a
274        custom one, because of the following reported problem in Windows:
276          - libbz2 uses the Pascal calling convention (WINAPI) for the functions
277              under Win32.
278          - The standard autoconf AC_CHECK_LIB fails to include "bzlib.h",
279              therefore missing the function definition.
280          - The compiler thus generates a "C" signature for the test function.
281          - The linker fails to find the "C" function.
282          - PCRE fails to configure if asked to do so against libbz2.
284    11. When running libtoolize from libtool-2.2.6b as part of autogen.sh, these
285        messages were output:
287          Consider adding `AC_CONFIG_MACRO_DIR([m4])' to configure.ac and
288          rerunning libtoolize, to keep the correct libtool macros in-tree.
289          Consider adding `-I m4' to ACLOCAL_AMFLAGS in Makefile.am.
291        I have done both of these things.
293    12. Although pcre_dfa_exec() does not use nearly as much stack as pcre_exec()
294        most of the time, it *can* run out if it is given a pattern that contains a
295        runaway infinite recursion. I updated the discussion in the pcrestack man
296        page.
298    13. Now that we have gone to the x.xx style of version numbers, the minor
299        version may start with zero. Using 08 or 09 is a bad idea because users
300        might check the value of PCRE_MINOR in their code, and 08 or 09 may be
301        interpreted as invalid octal numbers. I've updated the previous comment in
302        configure.ac, and also added a check that gives an error if 08 or 09 are
303        used.
305    14. Change 8.00/11 was not quite complete: code had been accidentally omitted,
306        causing partial matching to fail when the end of the subject matched \W
307        in a UTF-8 pattern where \W was quantified with a minimum of 3.
309    15. There were some discrepancies between the declarations in pcre_internal.h
310        of _pcre_is_newline(), _pcre_was_newline(), and _pcre_valid_utf8() and
311        their definitions. The declarations used "const uschar *" and the
312        definitions used USPTR. Even though USPTR is normally defined as "const
313        unsigned char *" (and uschar is typedeffed as "unsigned char"), it was
314        reported that: "This difference in casting confuses some C++ compilers, for
315        example, SunCC recognizes above declarations as different functions and
316        generates broken code for hbpcre." I have changed the declarations to use
317        USPTR.
319    16. GNU libtool is named differently on some systems. The autogen.sh script now
320        tries several variants such as glibtoolize (MacOSX) and libtoolize1x
321        (FreeBSD).
323    17. Applied Craig's patch that fixes an HP aCC compile error in pcre 8.00
324        (strtoXX undefined when compiling pcrecpp.cc). The patch contains this
325        comment: "Figure out how to create a longlong from a string: strtoll and
326        equivalent. It's not enough to call AC_CHECK_FUNCS: hpux has a strtoll, for
327        instance, but it only takes 2 args instead of 3!"
329    18. A subtle bug concerned with back references has been fixed by a change of
330        specification, with a corresponding code fix. A pattern such as
331        ^(xa|=?\1a)+$ which contains a back reference inside the group to which it
332        refers, was giving matches when it shouldn't. For example, xa=xaaa would
333        match that pattern. Interestingly, Perl (at least up to 5.11.3) has the
334        same bug. Such groups have to be quantified to be useful, or contained
335        inside another quantified group. (If there's no repetition, the reference
336        can never match.) The problem arises because, having left the group and
337        moved on to the rest of the pattern, a later failure that backtracks into
338        the group uses the captured value from the final iteration of the group
339        rather than the correct earlier one. I have fixed this in PCRE by forcing
340        any group that contains a reference to itself to be an atomic group; that
341        is, there cannot be any backtracking into it once it has completed. This is
342        similar to recursive and subroutine calls.
345    Version 8.00 19-Oct-09
346  ----------------------  ----------------------
348  1.  The table for translating pcre_compile() error codes into POSIX error codes  1.  The table for translating pcre_compile() error codes into POSIX error codes
349      was out-of-date, and there was no check on the pcre_compile() error code      was out-of-date, and there was no check on the pcre_compile() error code
350      being within the table. This could lead to an OK return being given in      being within the table. This could lead to an OK return being given in
351      error.      error.
353  2.  Changed the call to open a subject file in pcregrep from fopen(pathname,  2.  Changed the call to open a subject file in pcregrep from fopen(pathname,
354      "r") to fopen(pathname, "rb"), which fixed a problem with some of the tests      "r") to fopen(pathname, "rb"), which fixed a problem with some of the tests
355      in a Windows environment.      in a Windows environment.
357  3.  The pcregrep --count option prints the count for each file even when it is  3.  The pcregrep --count option prints the count for each file even when it is
358      zero, as does GNU grep. However, pcregrep was also printing all files when      zero, as does GNU grep. However, pcregrep was also printing all files when
359      --files-with-matches was added. Now, when both options are given, it prints      --files-with-matches was added. Now, when both options are given, it prints
360      counts only for those files that have at least one match. (GNU grep just      counts only for those files that have at least one match. (GNU grep just
361      prints the file name in this circumstance, but including the count seems      prints the file name in this circumstance, but including the count seems
362      more useful - otherwise, why use --count?) Also ensured that the      more useful - otherwise, why use --count?) Also ensured that the
363      combination -clh just lists non-zero counts, with no names.      combination -clh just lists non-zero counts, with no names.
365  4.  The long form of the pcregrep -F option was incorrectly implemented as  4.  The long form of the pcregrep -F option was incorrectly implemented as
366      --fixed_strings instead of --fixed-strings. This is an incompatible change,      --fixed_strings instead of --fixed-strings. This is an incompatible change,
367      but it seems right to fix it, and I didn't think it was worth preserving      but it seems right to fix it, and I didn't think it was worth preserving
368      the old behaviour.      the old behaviour.
370  5.  The command line items --regex=pattern and --regexp=pattern were not  5.  The command line items --regex=pattern and --regexp=pattern were not
371      recognized by pcregrep, which required --regex pattern or --regexp pattern      recognized by pcregrep, which required --regex pattern or --regexp pattern
372      (with a space rather than an '='). The man page documented the '=' forms,      (with a space rather than an '='). The man page documented the '=' forms,
373      which are compatible with GNU grep; these now work.      which are compatible with GNU grep; these now work.
375    6.  No libpcreposix.pc file was created for pkg-config; there was just
376        libpcre.pc and libpcrecpp.pc. The omission has been rectified.
378    7.  Added #ifndef SUPPORT_UCP into the pcre_ucd.c module, to reduce its size
379        when UCP support is not needed, by modifying the Python script that
380        generates it from Unicode data files. This should not matter if the module
381        is correctly used as a library, but I received one complaint about 50K of
382        unwanted data. My guess is that the person linked everything into his
383        program rather than using a library. Anyway, it does no harm.
385    8.  A pattern such as /\x{123}{2,2}+/8 was incorrectly compiled; the trigger
386        was a minimum greater than 1 for a wide character in a possessive
387        repetition. The same bug could also affect patterns like /(\x{ff}{0,2})*/8
388        which had an unlimited repeat of a nested, fixed maximum repeat of a wide
389        character. Chaos in the form of incorrect output or a compiling loop could
390        result.
392    9.  The restrictions on what a pattern can contain when partial matching is
393        requested for pcre_exec() have been removed. All patterns can now be
394        partially matched by this function. In addition, if there are at least two
395        slots in the offset vector, the offset of the earliest inspected character
396        for the match and the offset of the end of the subject are set in them when
397        PCRE_ERROR_PARTIAL is returned.
399    10. Partial matching has been split into two forms: PCRE_PARTIAL_SOFT, which is
400        synonymous with PCRE_PARTIAL, for backwards compatibility, and
401        PCRE_PARTIAL_HARD, which causes a partial match to supersede a full match,
402        and may be more useful for multi-segment matching.
404    11. Partial matching with pcre_exec() is now more intuitive. A partial match
405        used to be given if ever the end of the subject was reached; now it is
406        given only if matching could not proceed because another character was
407        needed. This makes a difference in some odd cases such as Z(*FAIL) with the
408        string "Z", which now yields "no match" instead of "partial match". In the
409        case of pcre_dfa_exec(), "no match" is given if every matching path for the
410        final character ended with (*FAIL).
412    12. Restarting a match using pcre_dfa_exec() after a partial match did not work
413        if the pattern had a "must contain" character that was already found in the
414        earlier partial match, unless partial matching was again requested. For
415        example, with the pattern /dog.(body)?/, the "must contain" character is
416        "g". If the first part-match was for the string "dog", restarting with
417        "sbody" failed. This bug has been fixed.
419    13. The string returned by pcre_dfa_exec() after a partial match has been
420        changed so that it starts at the first inspected character rather than the
421        first character of the match. This makes a difference only if the pattern
422        starts with a lookbehind assertion or \b or \B (\K is not supported by
423        pcre_dfa_exec()). It's an incompatible change, but it makes the two
424        matching functions compatible, and I think it's the right thing to do.
426    14. Added a pcredemo man page, created automatically from the pcredemo.c file,
427        so that the demonstration program is easily available in environments where
428        PCRE has not been installed from source.
430    15. Arranged to add -DPCRE_STATIC to cflags in libpcre.pc, libpcreposix.cp,
431        libpcrecpp.pc and pcre-config when PCRE is not compiled as a shared
432        library.
434    16. Added REG_UNGREEDY to the pcreposix interface, at the request of a user.
435        It maps to PCRE_UNGREEDY. It is not, of course, POSIX-compatible, but it
436        is not the first non-POSIX option to be added. Clearly some people find
437        these options useful.
439    17. If a caller to the POSIX matching function regexec() passes a non-zero
440        value for nmatch with a NULL value for pmatch, the value of
441        nmatch is forced to zero.
443    18. RunGrepTest did not have a test for the availability of the -u option of
444        the diff command, as RunTest does. It now checks in the same way as
445        RunTest, and also checks for the -b option.
447    19. If an odd number of negated classes containing just a single character
448        interposed, within parentheses, between a forward reference to a named
449        subpattern and the definition of the subpattern, compilation crashed with
450        an internal error, complaining that it could not find the referenced
451        subpattern. An example of a crashing pattern is /(?&A)(([^m])(?<A>))/.
452        [The bug was that it was starting one character too far in when skipping
453        over the character class, thus treating the ] as data rather than
454        terminating the class. This meant it could skip too much.]
456    20. Added PCRE_NOTEMPTY_ATSTART in order to be able to correctly implement the
457        /g option in pcretest when the pattern contains \K, which makes it possible
458        to have an empty string match not at the start, even when the pattern is
459        anchored. Updated pcretest and pcredemo to use this option.
461    21. If the maximum number of capturing subpatterns in a recursion was greater
462        than the maximum at the outer level, the higher number was returned, but
463        with unset values at the outer level. The correct (outer level) value is
464        now given.
466    22. If (*ACCEPT) appeared inside capturing parentheses, previous releases of
467        PCRE did not set those parentheses (unlike Perl). I have now found a way to
468        make it do so. The string so far is captured, making this feature
469        compatible with Perl.
471    23. The tests have been re-organized, adding tests 11 and 12, to make it
472        possible to check the Perl 5.10 features against Perl 5.10.
474    24. Perl 5.10 allows subroutine calls in lookbehinds, as long as the subroutine
475        pattern matches a fixed length string. PCRE did not allow this; now it
476        does. Neither allows recursion.
478    25. I finally figured out how to implement a request to provide the minimum
479        length of subject string that was needed in order to match a given pattern.
480        (It was back references and recursion that I had previously got hung up
481        on.) This code has now been added to pcre_study(); it finds a lower bound
482        to the length of subject needed. It is not necessarily the greatest lower
483        bound, but using it to avoid searching strings that are too short does give
484        some useful speed-ups. The value is available to calling programs via
485        pcre_fullinfo().
487    26. While implementing 25, I discovered to my embarrassment that pcretest had
488        not been passing the result of pcre_study() to pcre_dfa_exec(), so the
489        study optimizations had never been tested with that matching function.
490        Oops. What is worse, even when it was passed study data, there was a bug in
491        pcre_dfa_exec() that meant it never actually used it. Double oops. There
492        were also very few tests of studied patterns with pcre_dfa_exec().
494    27. If (?| is used to create subpatterns with duplicate numbers, they are now
495        allowed to have the same name, even if PCRE_DUPNAMES is not set. However,
496        on the other side of the coin, they are no longer allowed to have different
497        names, because these cannot be distinguished in PCRE, and this has caused
498        confusion. (This is a difference from Perl.)
500    28. When duplicate subpattern names are present (necessarily with different
501        numbers, as required by 27 above), and a test is made by name in a
502        conditional pattern, either for a subpattern having been matched, or for
503        recursion in such a pattern, all the associated numbered subpatterns are
504        tested, and the overall condition is true if the condition is true for any
505        one of them. This is the way Perl works, and is also more like the way
506        testing by number works.
509  Version 7.9 11-Apr-09  Version 7.9 11-Apr-09
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