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1  ChangeLog for PCRE  ChangeLog for PCRE
2  ------------------  ------------------
3    
4  Version 8.00 ??-???-??  Version 8.10 03 May-2010
5    ------------------------
6    
7    1.  Added support for (*MARK:ARG) and for ARG additions to PRUNE, SKIP, and
8        THEN.
9    
10    2.  (*ACCEPT) was not working when inside an atomic group.
11    
12    3.  Inside a character class, \B is treated as a literal by default, but
13        faulted if PCRE_EXTRA is set. This mimics Perl's behaviour (the -w option
14        causes the error). The code is unchanged, but I tidied the documentation.
15    
16    4.  Inside a character class, PCRE always treated \R and \X as literals,
17        whereas Perl faults them if its -w option is set. I have changed PCRE so
18        that it faults them when PCRE_EXTRA is set.
19    
20    5.  Added support for \N, which always matches any character other than
21        newline. (It is the same as "." when PCRE_DOTALL is not set.)
22    
23    6.  When compiling pcregrep with newer versions of gcc which may have
24        FORTIFY_SOURCE set, several warnings "ignoring return value of 'fwrite',
25        declared with attribute warn_unused_result" were given. Just casting the
26        result to (void) does not stop the warnings; a more elaborate fudge is
27        needed. I've used a macro to implement this.
28    
29    7.  Minor change to pcretest.c to avoid a compiler warning.
30    
31    8.  Added four artifical Unicode properties to help with an option to make
32        \s etc use properties (see next item). The new properties are: Xan
33        (alphanumeric), Xsp (Perl space), Xps (POSIX space), and Xwd (word).
34    
35    9.  Added PCRE_UCP to make \b, \d, \s, \w, and certain POSIX character classes
36        use Unicode properties. (*UCP) at the start of a pattern can be used to set
37        this option. Modified pcretest to add /W to test this facility. Added
38        REG_UCP to make it available via the POSIX interface.
39    
40    10. Added --line-buffered to pcregrep.
41    
42    11. In UTF-8 mode, if a pattern that was compiled with PCRE_CASELESS was
43        studied, and the match started with a letter with a code point greater than
44        127 whose first byte was different to the first byte of the other case of
45        the letter, the other case of this starting letter was not recognized.
46    
47    12. pcreposix.c included pcre.h before including pcre_internal.h. This caused a
48        conflict in the definition of PCRE_EXP_DECL. I have removed the include of
49        pcre.h as pcre_internal.h includes pcre.h itself. (This may be a bit of
50        historical tidying that never got done.)
51    
52    13. If a pattern that was studied started with a repeated Unicode property
53        test, for example, \p{Nd}+, there was the theoretical possibility of
54        setting up an incorrect bitmap of starting bytes, but fortunately it could
55        not have actually happened in practice until change 8 above was made (it
56        added property types that matched character-matching opcodes).
57    
58    14. pcre_study() now recognizes \h, \v, and \R when constructing a bit map of
59        possible starting bytes for non-anchored patterns.
60    
61    15. The "auto-possessify" feature of pcre_compile() now recognizes \R.
62    
63    16. If a repeated Unicode property match (e.g. \p{Lu}*) was used with non-UTF-8
64        input, it could crash or give wrong results if characters with values
65        greater than 0xc0 were present in the subject string. (Detail: it assumed
66        UTF-8 input when processing these items.)
67    
68    17. Added a lot of (int) casts to avoid compiler warnings in systems where
69        size_t is 64-bit.
70    
71    
72    
73    Version 8.02 19-Mar-2010
74    ------------------------
75    
76    1.  The Unicode data tables have been updated to Unicode 5.2.0.
77    
78    2.  Added the option --libs-cpp to pcre-config, but only when C++ support is
79        configured.
80    
81    3.  Updated the licensing terms in the pcregexp.pas file, as agreed with the
82        original author of that file, following a query about its status.
83    
84    4.  On systems that do not have stdint.h (e.g. Solaris), check for and include
85        inttypes.h instead. This fixes a bug that was introduced by change 8.01/8.
86    
87    5.  A pattern such as (?&t)*+(?(DEFINE)(?<t>.)) which has a possessive
88        quantifier applied to a forward-referencing subroutine call, could compile
89        incorrect code or give the error "internal error: previously-checked
90        referenced subpattern not found".
91    
92    6.  Both MS Visual Studio and Symbian OS have problems with initializing
93        variables to point to external functions. For these systems, therefore,
94        pcre_malloc etc. are now initialized to local functions that call the
95        relevant global functions.
96    
97    7.  There were two entries missing in the vectors called coptable and poptable
98        in pcre_dfa_exec.c. This could lead to memory accesses outsize the vectors.
99        I've fixed the data, and added a kludgy way of testing at compile time that
100        the lengths are correct (equal to the number of opcodes).
101    
102    8.  Following on from 7, I added a similar kludge to check the length of the
103        eint vector in pcreposix.c.
104    
105    9.  Error texts for pcre_compile() are held as one long string to avoid too
106        much relocation at load time. To find a text, the string is searched,
107        counting zeros. There was no check for running off the end of the string,
108        which could happen if a new error number was added without updating the
109        string.
110    
111    10. \K gave a compile-time error if it appeared in a lookbehind assersion.
112    
113    11. \K was not working if it appeared in an atomic group or in a group that
114        was called as a "subroutine", or in an assertion. Perl 5.11 documents that
115        \K is "not well defined" if used in an assertion. PCRE now accepts it if
116        the assertion is positive, but not if it is negative.
117    
118    12. Change 11 fortuitously reduced the size of the stack frame used in the
119        "match()" function of pcre_exec.c by one pointer. Forthcoming
120        implementation of support for (*MARK) will need an extra pointer on the
121        stack; I have reserved it now, so that the stack frame size does not
122        decrease.
123    
124    13. A pattern such as (?P<L1>(?P<L2>0)|(?P>L2)(?P>L1)) in which the only other
125        item in branch that calls a recursion is a subroutine call - as in the
126        second branch in the above example - was incorrectly given the compile-
127        time error "recursive call could loop indefinitely" because pcre_compile()
128        was not correctly checking the subroutine for matching a non-empty string.
129    
130    14. The checks for overrunning compiling workspace could trigger after an
131        overrun had occurred. This is a "should never occur" error, but it can be
132        triggered by pathological patterns such as hundreds of nested parentheses.
133        The checks now trigger 100 bytes before the end of the workspace.
134    
135    15. Fix typo in configure.ac: "srtoq" should be "strtoq".
136    
137    
138    Version 8.01 19-Jan-2010
139    ------------------------
140    
141    1.  If a pattern contained a conditional subpattern with only one branch (in
142        particular, this includes all (*DEFINE) patterns), a call to pcre_study()
143        computed the wrong minimum data length (which is of course zero for such
144        subpatterns). This could cause incorrect "no match" results.
145    
146    2.  For patterns such as (?i)a(?-i)b|c where an option setting at the start of
147        the pattern is reset in the first branch, pcre_compile() failed with
148        "internal error: code overflow at offset...". This happened only when
149        the reset was to the original external option setting. (An optimization
150        abstracts leading options settings into an external setting, which was the
151        cause of this.)
152    
153    3.  A pattern such as ^(?!a(*SKIP)b) where a negative assertion contained one
154        of the verbs SKIP, PRUNE, or COMMIT, did not work correctly. When the
155        assertion pattern did not match (meaning that the assertion was true), it
156        was incorrectly treated as false if the SKIP had been reached during the
157        matching. This also applied to assertions used as conditions.
158    
159    4.  If an item that is not supported by pcre_dfa_exec() was encountered in an
160        assertion subpattern, including such a pattern used as a condition,
161        unpredictable results occurred, instead of the error return
162        PCRE_ERROR_DFA_UITEM.
163    
164    5.  The C++ GlobalReplace function was not working like Perl for the special
165        situation when an empty string is matched. It now does the fancy magic
166        stuff that is necessary.
167    
168    6.  In pcre_internal.h, obsolete includes to setjmp.h and stdarg.h have been
169        removed. (These were left over from very, very early versions of PCRE.)
170    
171    7.  Some cosmetic changes to the code to make life easier when compiling it
172        as part of something else:
173    
174        (a) Change DEBUG to PCRE_DEBUG.
175    
176        (b) In pcre_compile(), rename the member of the "branch_chain" structure
177            called "current" as "current_branch", to prevent a collision with the
178            Linux macro when compiled as a kernel module.
179    
180        (c) In pcre_study(), rename the function set_bit() as set_table_bit(), to
181            prevent a collision with the Linux macro when compiled as a kernel
182            module.
183    
184    8.  In pcre_compile() there are some checks for integer overflows that used to
185        cast potentially large values to (double). This has been changed to that
186        when building, a check for int64_t is made, and if it is found, it is used
187        instead, thus avoiding the use of floating point arithmetic. (There is no
188        other use of FP in PCRE.) If int64_t is not found, the fallback is to
189        double.
190    
191    9.  Added two casts to avoid signed/unsigned warnings from VS Studio Express
192        2005 (difference between two addresses compared to an unsigned value).
193    
194    10. Change the standard AC_CHECK_LIB test for libbz2 in configure.ac to a
195        custom one, because of the following reported problem in Windows:
196    
197          - libbz2 uses the Pascal calling convention (WINAPI) for the functions
198              under Win32.
199          - The standard autoconf AC_CHECK_LIB fails to include "bzlib.h",
200              therefore missing the function definition.
201          - The compiler thus generates a "C" signature for the test function.
202          - The linker fails to find the "C" function.
203          - PCRE fails to configure if asked to do so against libbz2.
204    
205    11. When running libtoolize from libtool-2.2.6b as part of autogen.sh, these
206        messages were output:
207    
208          Consider adding `AC_CONFIG_MACRO_DIR([m4])' to configure.ac and
209          rerunning libtoolize, to keep the correct libtool macros in-tree.
210          Consider adding `-I m4' to ACLOCAL_AMFLAGS in Makefile.am.
211    
212        I have done both of these things.
213    
214    12. Although pcre_dfa_exec() does not use nearly as much stack as pcre_exec()
215        most of the time, it *can* run out if it is given a pattern that contains a
216        runaway infinite recursion. I updated the discussion in the pcrestack man
217        page.
218    
219    13. Now that we have gone to the x.xx style of version numbers, the minor
220        version may start with zero. Using 08 or 09 is a bad idea because users
221        might check the value of PCRE_MINOR in their code, and 08 or 09 may be
222        interpreted as invalid octal numbers. I've updated the previous comment in
223        configure.ac, and also added a check that gives an error if 08 or 09 are
224        used.
225    
226    14. Change 8.00/11 was not quite complete: code had been accidentally omitted,
227        causing partial matching to fail when the end of the subject matched \W
228        in a UTF-8 pattern where \W was quantified with a minimum of 3.
229    
230    15. There were some discrepancies between the declarations in pcre_internal.h
231        of _pcre_is_newline(), _pcre_was_newline(), and _pcre_valid_utf8() and
232        their definitions. The declarations used "const uschar *" and the
233        definitions used USPTR. Even though USPTR is normally defined as "const
234        unsigned char *" (and uschar is typedeffed as "unsigned char"), it was
235        reported that: "This difference in casting confuses some C++ compilers, for
236        example, SunCC recognizes above declarations as different functions and
237        generates broken code for hbpcre." I have changed the declarations to use
238        USPTR.
239    
240    16. GNU libtool is named differently on some systems. The autogen.sh script now
241        tries several variants such as glibtoolize (MacOSX) and libtoolize1x
242        (FreeBSD).
243    
244    17. Applied Craig's patch that fixes an HP aCC compile error in pcre 8.00
245        (strtoXX undefined when compiling pcrecpp.cc). The patch contains this
246        comment: "Figure out how to create a longlong from a string: strtoll and
247        equivalent. It's not enough to call AC_CHECK_FUNCS: hpux has a strtoll, for
248        instance, but it only takes 2 args instead of 3!"
249    
250    18. A subtle bug concerned with back references has been fixed by a change of
251        specification, with a corresponding code fix. A pattern such as
252        ^(xa|=?\1a)+$ which contains a back reference inside the group to which it
253        refers, was giving matches when it shouldn't. For example, xa=xaaa would
254        match that pattern. Interestingly, Perl (at least up to 5.11.3) has the
255        same bug. Such groups have to be quantified to be useful, or contained
256        inside another quantified group. (If there's no repetition, the reference
257        can never match.) The problem arises because, having left the group and
258        moved on to the rest of the pattern, a later failure that backtracks into
259        the group uses the captured value from the final iteration of the group
260        rather than the correct earlier one. I have fixed this in PCRE by forcing
261        any group that contains a reference to itself to be an atomic group; that
262        is, there cannot be any backtracking into it once it has completed. This is
263        similar to recursive and subroutine calls.
264    
265    
266    Version 8.00 19-Oct-09
267  ----------------------  ----------------------
268    
269  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
270      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
271      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
272      error.      error.
273    
274  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,
275      "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
276      in a Windows environment.      in a Windows environment.
277    
278  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
279      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
280      --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
281      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
282      prints the file name in this circumstance, but including the count seems      prints the file name in this circumstance, but including the count seems
283      more useful - otherwise, why use --count?) Also ensured that the      more useful - otherwise, why use --count?) Also ensured that the
284      combination -clh just lists non-zero counts, with no names.      combination -clh just lists non-zero counts, with no names.
285    
286  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
287      --fixed_strings instead of --fixed-strings. This is an incompatible change,      --fixed_strings instead of --fixed-strings. This is an incompatible change,
288      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
289      the old behaviour.      the old behaviour.
290    
291  5.  The command line items --regex=pattern and --regexp=pattern were not  5.  The command line items --regex=pattern and --regexp=pattern were not
292      recognized by pcregrep, which required --regex pattern or --regexp pattern      recognized by pcregrep, which required --regex pattern or --regexp pattern
293      (with a space rather than an '='). The man page documented the '=' forms,      (with a space rather than an '='). The man page documented the '=' forms,
294      which are compatible with GNU grep; these now work.      which are compatible with GNU grep; these now work.
295    
296  6.  No libpcreposix.pc file was created for pkg-config; there was just  6.  No libpcreposix.pc file was created for pkg-config; there was just
297      libpcre.pc and libpcrecpp.pc. The omission has been rectified.      libpcre.pc and libpcrecpp.pc. The omission has been rectified.
298    
299  7.  Added #ifndef SUPPORT_UCP into the pcre_ucd.c module, to reduce its size  7.  Added #ifndef SUPPORT_UCP into the pcre_ucd.c module, to reduce its size
300      when UCP support is not needed, by modifying the Python script that      when UCP support is not needed, by modifying the Python script that
301      generates it from Unicode data files. This should not matter if the module      generates it from Unicode data files. This should not matter if the module
302      is correctly used as a library, but I received one complaint about 50K of      is correctly used as a library, but I received one complaint about 50K of
303      unwanted data. My guess is that the person linked everything into his      unwanted data. My guess is that the person linked everything into his
304      program rather than using a library. Anyway, it does no harm.      program rather than using a library. Anyway, it does no harm.
305    
306  8.  A pattern such as /\x{123}{2,2}+/8 was incorrectly compiled; the trigger  8.  A pattern such as /\x{123}{2,2}+/8 was incorrectly compiled; the trigger
307      was a minimum greater than 1 for a wide character in a possessive      was a minimum greater than 1 for a wide character in a possessive
308      repetition. The same bug could also affect patterns like /(\x{ff}{0,2})*/8      repetition. The same bug could also affect patterns like /(\x{ff}{0,2})*/8
309      which had an unlimited repeat of a nested, fixed maximum repeat of a wide      which had an unlimited repeat of a nested, fixed maximum repeat of a wide
310      character. Chaos in the form of incorrect output or a compiling loop could      character. Chaos in the form of incorrect output or a compiling loop could
311      result.      result.
312    
313  9.  The restrictions on what a pattern can contain when partial matching is  9.  The restrictions on what a pattern can contain when partial matching is
314      requested for pcre_exec() have been removed. All patterns can now be      requested for pcre_exec() have been removed. All patterns can now be
315      partially matched by this function. In addition, if there are at least two      partially matched by this function. In addition, if there are at least two
316      slots in the offset vector, the offset of the earliest inspected character      slots in the offset vector, the offset of the earliest inspected character
317      for the match and the offset of the end of the subject are set in them when      for the match and the offset of the end of the subject are set in them when
318      PCRE_ERROR_PARTIAL is returned.      PCRE_ERROR_PARTIAL is returned.
319    
320  10. Partial matching has been split into two forms: PCRE_PARTIAL_SOFT, which is  10. Partial matching has been split into two forms: PCRE_PARTIAL_SOFT, which is
321      synonymous with PCRE_PARTIAL, for backwards compatibility, and      synonymous with PCRE_PARTIAL, for backwards compatibility, and
322      PCRE_PARTIAL_HARD, which causes a partial match to supersede a full match,      PCRE_PARTIAL_HARD, which causes a partial match to supersede a full match,
323      and may be more useful for multi-segment matching, especially with      and may be more useful for multi-segment matching.
324      pcre_exec().  
325    11. Partial matching with pcre_exec() is now more intuitive. A partial match
326  11. Partial matching with pcre_exec() is now more intuitive. A partial match      used to be given if ever the end of the subject was reached; now it is
327      used to be given if ever the end of the subject was reached; now it is      given only if matching could not proceed because another character was
328      given only if matching could not proceed because another character was      needed. This makes a difference in some odd cases such as Z(*FAIL) with the
329      needed. This makes a difference in some odd cases such as Z(*FAIL) with the      string "Z", which now yields "no match" instead of "partial match". In the
330      string "Z", which now yields "no match" instead of "partial match". In the      case of pcre_dfa_exec(), "no match" is given if every matching path for the
331      case of pcre_dfa_exec(), "no match" is given if every matching path for the      final character ended with (*FAIL).
332      final character ended with (*FAIL).  
   
333  12. Restarting a match using pcre_dfa_exec() after a partial match did not work  12. Restarting a match using pcre_dfa_exec() after a partial match did not work
334      if the pattern had a "must contain" character that was already found in the      if the pattern had a "must contain" character that was already found in the
335      earlier partial match, unless partial matching was again requested. For      earlier partial match, unless partial matching was again requested. For
336      example, with the pattern /dog.(body)?/, the "must contain" character is      example, with the pattern /dog.(body)?/, the "must contain" character is
337      "g". If the first part-match was for the string "dog", restarting with      "g". If the first part-match was for the string "dog", restarting with
338      "sbody" failed. This bug has been fixed.      "sbody" failed. This bug has been fixed.
339    
340  13. The string returned by pcre_dfa_exec() after a partial match has been  13. The string returned by pcre_dfa_exec() after a partial match has been
341      changed so that it starts at the first inspected character rather than the      changed so that it starts at the first inspected character rather than the
342      first character of the match. This makes a difference only if the pattern      first character of the match. This makes a difference only if the pattern
343      starts with a lookbehind assertion or \b or \B (\K is not supported by      starts with a lookbehind assertion or \b or \B (\K is not supported by
344      pcre_dfa_exec()). It's an incompatible change, but it makes the two      pcre_dfa_exec()). It's an incompatible change, but it makes the two
345      matching functions compatible, and I think it's the right thing to do.      matching functions compatible, and I think it's the right thing to do.
346    
347  14. Added a pcredemo man page, created automatically from the pcredemo.c file,  14. Added a pcredemo man page, created automatically from the pcredemo.c file,
348      so that the demonstration program is easily available in environments where      so that the demonstration program is easily available in environments where
349      PCRE has not been installed from source.      PCRE has not been installed from source.
350    
351  15. Arranged to add -DPCRE_STATIC to cflags in libpcre.pc, libpcreposix.cp,  15. Arranged to add -DPCRE_STATIC to cflags in libpcre.pc, libpcreposix.cp,
352      libpcrecpp.pc and pcre-config when PCRE is not compiled as a shared      libpcrecpp.pc and pcre-config when PCRE is not compiled as a shared
353      library.      library.
354    
355  16. Added REG_UNGREEDY to the pcreposix interface, at the request of a user.  16. Added REG_UNGREEDY to the pcreposix interface, at the request of a user.
356      It maps to PCRE_UNGREEDY. It is not, of course, POSIX-compatible, but it      It maps to PCRE_UNGREEDY. It is not, of course, POSIX-compatible, but it
357      is not the first non-POSIX option to be added. Clearly some people find      is not the first non-POSIX option to be added. Clearly some people find
358      these options useful.      these options useful.
359    
360  17. If a caller to the POSIX matching function regexec() passes a non-zero  17. If a caller to the POSIX matching function regexec() passes a non-zero
361      value for nmatch with a NULL value for pmatch, the value of      value for nmatch with a NULL value for pmatch, the value of
362      nmatch is forced to zero.      nmatch is forced to zero.
363    
364  18. RunGrepTest did not have a test for the availability of the -u option of  18. RunGrepTest did not have a test for the availability of the -u option of
365      the diff command, as RunTest does. It now checks in the same way as      the diff command, as RunTest does. It now checks in the same way as
366      RunTest, and also checks for the -b option.      RunTest, and also checks for the -b option.
367    
368  19. If an odd number of negated classes containing just a single character  19. If an odd number of negated classes containing just a single character
369      interposed, within parentheses, between a forward reference to a named      interposed, within parentheses, between a forward reference to a named
370      subpattern and the definition of the subpattern, compilation crashed with      subpattern and the definition of the subpattern, compilation crashed with
371      an internal error, complaining that it could not find the referenced      an internal error, complaining that it could not find the referenced
372      subpattern. An example of a crashing pattern is /(?&A)(([^m])(?<A>))/.      subpattern. An example of a crashing pattern is /(?&A)(([^m])(?<A>))/.
373      [The bug was that it was starting one character too far in when skipping      [The bug was that it was starting one character too far in when skipping
374      over the character class, thus treating the ] as data rather than      over the character class, thus treating the ] as data rather than
375      terminating the class. This meant it could skip too much.]      terminating the class. This meant it could skip too much.]
376    
377  20. Added PCRE_NOTEMPTY_ATSTART in order to be able to correctly implement the  20. Added PCRE_NOTEMPTY_ATSTART in order to be able to correctly implement the
378      /g option in pcretest when the pattern contains \K, which makes it possible      /g option in pcretest when the pattern contains \K, which makes it possible
379      to have an empty string match not at the start, even when the pattern is      to have an empty string match not at the start, even when the pattern is
380      anchored. Updated pcretest and pcredemo to use this option.      anchored. Updated pcretest and pcredemo to use this option.
381    
382  21. If the maximum number of capturing subpatterns in a recursion was greater  21. If the maximum number of capturing subpatterns in a recursion was greater
383      than the maximum at the outer level, the higher number was returned, but      than the maximum at the outer level, the higher number was returned, but
384      with unset values at the outer level. The correct (outer level) value is      with unset values at the outer level. The correct (outer level) value is
385      now given.      now given.
386    
387  22. If (*ACCEPT) appeared inside capturing parentheses, previous releases of  22. If (*ACCEPT) appeared inside capturing parentheses, previous releases of
388      PCRE did not set those parentheses (unlike Perl). I have now found a way to      PCRE did not set those parentheses (unlike Perl). I have now found a way to
389      make it do so. The string so far is captured, making this feature      make it do so. The string so far is captured, making this feature
390      compatible with Perl.      compatible with Perl.
391    
392  23. The tests have been re-organized, adding tests 11 and 12, to make it  23. The tests have been re-organized, adding tests 11 and 12, to make it
393      possible to check the Perl 5.10 features against Perl 5.10.      possible to check the Perl 5.10 features against Perl 5.10.
394    
395  24. Perl 5.10 allows subroutine calls in lookbehinds, as long as the subroutine  24. Perl 5.10 allows subroutine calls in lookbehinds, as long as the subroutine
396      pattern matches a fixed length string. PCRE did not allow this; now it      pattern matches a fixed length string. PCRE did not allow this; now it
397      does. Neither allows recursion.      does. Neither allows recursion.
398    
399    25. I finally figured out how to implement a request to provide the minimum
400        length of subject string that was needed in order to match a given pattern.
401        (It was back references and recursion that I had previously got hung up
402        on.) This code has now been added to pcre_study(); it finds a lower bound
403        to the length of subject needed. It is not necessarily the greatest lower
404        bound, but using it to avoid searching strings that are too short does give
405        some useful speed-ups. The value is available to calling programs via
406        pcre_fullinfo().
407    
408    26. While implementing 25, I discovered to my embarrassment that pcretest had
409        not been passing the result of pcre_study() to pcre_dfa_exec(), so the
410        study optimizations had never been tested with that matching function.
411        Oops. What is worse, even when it was passed study data, there was a bug in
412        pcre_dfa_exec() that meant it never actually used it. Double oops. There
413        were also very few tests of studied patterns with pcre_dfa_exec().
414    
415    27. If (?| is used to create subpatterns with duplicate numbers, they are now
416        allowed to have the same name, even if PCRE_DUPNAMES is not set. However,
417        on the other side of the coin, they are no longer allowed to have different
418        names, because these cannot be distinguished in PCRE, and this has caused
419        confusion. (This is a difference from Perl.)
420    
421    28. When duplicate subpattern names are present (necessarily with different
422        numbers, as required by 27 above), and a test is made by name in a
423        conditional pattern, either for a subpattern having been matched, or for
424        recursion in such a pattern, all the associated numbered subpatterns are
425        tested, and the overall condition is true if the condition is true for any
426        one of them. This is the way Perl works, and is also more like the way
427        testing by number works.
428    
429    
430  Version 7.9 11-Apr-09  Version 7.9 11-Apr-09
431  ---------------------  ---------------------

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