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

Diff of /code/trunk/doc/pcre.txt

Parent Directory | Revision Log | View Patch Patch

-revision 41 by nigel,
Sat Feb 24 21:39:17 2007 UTC
+revision 155 by ph10,
Tue Apr 24 13:36:11 2007 UTC
 Line 1
+ -----------------------------------------------------------------------------
+ This file contains a concatenation of the PCRE man pages, converted to plain
+ text format for ease of searching with a text editor, or for use on systems
+ that do not have a man page processor. The small individual files that give
+ synopses of each function in the library have not been included. There are
+ separate text files for the pcregrep and pcretest commands.
+ -----------------------------------------------------------------------------
+ PCRE(3)                                                                PCRE(3)
  NAME
-      pcre - Perl-compatible regular expressions.
+        PCRE - Perl-compatible regular expressions
+ INTRODUCTION
- SYNOPSIS
+        The  PCRE  library is a set of functions that implement regular expres-
-      #include <pcre.h>
+        sion pattern matching using the same syntax and semantics as Perl, with
+        just  a  few differences. (Certain features that appeared in Python and
+        PCRE before they appeared in Perl are also available using  the  Python
+        syntax.)
+        The  current  implementation of PCRE (release 7.x) corresponds approxi-
+        mately with Perl 5.10, including support for UTF-8 encoded strings  and
+        Unicode general category properties. However, UTF-8 and Unicode support
+        has to be explicitly enabled; it is not the default. The Unicode tables
+        correspond to Unicode release 5.0.0.
+        In  addition to the Perl-compatible matching function, PCRE contains an
+        alternative matching function that matches the same  compiled  patterns
+        in  a different way. In certain circumstances, the alternative function
+        has some advantages. For a discussion of the two  matching  algorithms,
+        see the pcrematching page.
+        PCRE  is  written  in C and released as a C library. A number of people
+        have written wrappers and interfaces of various kinds.  In  particular,
+        Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
+        included as part of the PCRE distribution. The pcrecpp page has details
+        of  this  interface.  Other  people's contributions can be found in the
+        Contrib directory at the primary FTP site, which is:
+        ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
+        Details of exactly which Perl regular expression features are  and  are
+        not supported by PCRE are given in separate documents. See the pcrepat-
+        tern and pcrecompat pages.
+        Some features of PCRE can be included, excluded, or  changed  when  the
+        library  is  built.  The pcre_config() function makes it possible for a
+        client to discover which features are  available.  The  features  them-
+        selves  are described in the pcrebuild page. Documentation about build-
+        ing PCRE for various operating systems can be found in the README  file
+        in the source distribution.
+        The  library  contains  a number of undocumented internal functions and
+        data tables that are used by more than one  of  the  exported  external
+        functions,  but  which  are  not  intended for use by external callers.
+        Their names all begin with "_pcre_", which hopefully will  not  provoke
+        any name clashes. In some environments, it is possible to control which
+        external symbols are exported when a shared library is  built,  and  in
+        these cases the undocumented symbols are not exported.
+ USER DOCUMENTATION
+        The  user  documentation  for PCRE comprises a number of different sec-
+        tions. In the "man" format, each of these is a separate "man page".  In
+        the  HTML  format, each is a separate page, linked from the index page.
+        In the plain text format, all the sections are concatenated,  for  ease
+        of searching. The sections are as follows:
+          pcre              this document
+          pcre-config       show PCRE installation configuration information
+          pcreapi           details of PCRE's native C API
+          pcrebuild         options for building PCRE
+          pcrecallout       details of the callout feature
+          pcrecompat        discussion of Perl compatibility
+          pcrecpp           details of the C++ wrapper
+          pcregrep          description of the pcregrep command
+          pcrematching      discussion of the two matching algorithms
+          pcrepartial       details of the partial matching facility
+          pcrepattern       syntax and semantics of supported
+                              regular expressions
+          pcreperform       discussion of performance issues
+          pcreposix         the POSIX-compatible C API
+          pcreprecompile    details of saving and re-using precompiled patterns
+          pcresample        discussion of the sample program
+          pcrestack         discussion of stack usage
+          pcretest          description of the pcretest testing command
-      pcre *pcre_compile(const char *pattern, int options,
+        In addition, in the "man" and HTML formats, there is a short  page  for
-           const char **errptr, int *erroffset,
+        each C library function, listing its arguments and results.
-           const unsigned char *tableptr);
-      pcre_extra *pcre_study(const pcre *code, int options,
-           const char **errptr);
-      int pcre_exec(const pcre *code, const pcre_extra *extra,
+ LIMITATIONS
-           const char *subject, int length, int startoffset,
-           int options, int *ovector, int ovecsize);
+        There  are some size limitations in PCRE but it is hoped that they will
+        never in practice be relevant.
-      int pcre_copy_substring(const char *subject, int *ovector,
+        The maximum length of a compiled pattern is 65539 (sic) bytes  if  PCRE
-           int stringcount, int stringnumber, char *buffer,
+        is compiled with the default internal linkage size of 2. If you want to
-           int buffersize);
+        process regular expressions that are truly enormous,  you  can  compile
+        PCRE  with  an  internal linkage size of 3 or 4 (see the README file in
+        the source distribution and the pcrebuild documentation  for  details).
+        In  these  cases the limit is substantially larger.  However, the speed
+        of execution is slower.
+        All values in repeating quantifiers must be less than 65536. The  maxi-
+        mum  compiled  length  of  subpattern  with an explicit repeat count is
+bytes. The maximum number of capturing subpatterns is 65535.
+        There is no limit to the number of parenthesized subpatterns, but there
+        can be no more than 65535 capturing subpatterns.
+        The maximum length of name for a named subpattern is 32 characters, and
+        the maximum number of named subpatterns is 10000.
+        The maximum length of a subject string is the largest  positive  number
+        that  an integer variable can hold. However, when using the traditional
+        matching function, PCRE uses recursion to handle subpatterns and indef-
+        inite  repetition.  This means that the available stack space may limit
+        the size of a subject string that can be processed by certain patterns.
+        For a discussion of stack issues, see the pcrestack documentation.
+ UTF-8 AND UNICODE PROPERTY SUPPORT
+        From  release  3.3,  PCRE  has  had  some support for character strings
+        encoded in the UTF-8 format. For release 4.0 this was greatly  extended
+        to  cover  most common requirements, and in release 5.0 additional sup-
+        port for Unicode general category properties was added.
+        In order process UTF-8 strings, you must build PCRE  to  include  UTF-8
+        support  in  the  code,  and, in addition, you must call pcre_compile()
+        with the PCRE_UTF8 option flag. When you do this, both the pattern  and
+        any  subject  strings  that are matched against it are treated as UTF-8
+        strings instead of just strings of bytes.
+        If you compile PCRE with UTF-8 support, but do not use it at run  time,
+        the  library will be a bit bigger, but the additional run time overhead
+        is limited to testing the PCRE_UTF8 flag occasionally, so should not be
+        very big.
+        If PCRE is built with Unicode character property support (which implies
+        UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
+        ported.  The available properties that can be tested are limited to the
+        general category properties such as Lu for an upper case letter  or  Nd
+        for  a  decimal number, the Unicode script names such as Arabic or Han,
+        and the derived properties Any and L&. A full  list  is  given  in  the
+        pcrepattern documentation. Only the short names for properties are sup-
+        ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
+        ter},  is  not  supported.   Furthermore,  in Perl, many properties may
+        optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
+        does not support this.
+        The following comments apply when PCRE is running in UTF-8 mode:
+.  When you set the PCRE_UTF8 flag, the strings passed as patterns and
+        subjects are checked for validity on entry to the  relevant  functions.
+        If an invalid UTF-8 string is passed, an error return is given. In some
+        situations, you may already know  that  your  strings  are  valid,  and
+        therefore want to skip these checks in order to improve performance. If
+        you set the PCRE_NO_UTF8_CHECK flag at compile time  or  at  run  time,
+        PCRE  assumes  that  the  pattern or subject it is given (respectively)
+        contains only valid UTF-8 codes. In this case, it does not diagnose  an
+        invalid  UTF-8 string. If you pass an invalid UTF-8 string to PCRE when
+        PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program  may
+        crash.
+.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
+        two-byte UTF-8 character if the value is greater than 127.
+. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8
+        characters for values greater than \177.
+.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
+        vidual bytes, for example: \x{100}{3}.
+. The dot metacharacter matches one UTF-8 character instead of a  sin-
+        gle byte.
+.  The  escape sequence \C can be used to match a single byte in UTF-8
+        mode, but its use can lead to some strange effects.  This  facility  is
+        not available in the alternative matching function, pcre_dfa_exec().
+.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
+        test characters of any code value, but the characters that PCRE  recog-
+        nizes  as  digits,  spaces,  or  word characters remain the same set as
+        before, all with values less than 256. This remains true even when PCRE
+        includes  Unicode  property support, because to do otherwise would slow
+        down PCRE in many common cases. If you really want to test for a  wider
+        sense  of,  say,  "digit",  you must use Unicode property tests such as
+        \p{Nd}.
+. Similarly, characters that match the POSIX named  character  classes
+        are all low-valued characters.
+.  Case-insensitive  matching  applies only to characters whose values
+        are less than 128, unless PCRE is built with Unicode property  support.
+        Even  when  Unicode  property support is available, PCRE still uses its
+        own character tables when checking the case of  low-valued  characters,
+        so  as not to degrade performance.  The Unicode property information is
+        used only for characters with higher values. Even when Unicode property
+        support is available, PCRE supports case-insensitive matching only when
+        there is a one-to-one mapping between a letter's  cases.  There  are  a
+        small  number  of  many-to-one  mappings in Unicode; these are not sup-
+        ported by PCRE.
-      int pcre_get_substring(const char *subject, int *ovector,
-           int stringcount, int stringnumber,
-           const char **stringptr);
-      int pcre_get_substring_list(const char *subject,
+ AUTHOR
-           int *ovector, int stringcount, const char ***listptr);
-      const unsigned char *pcre_maketables(void);
+        Philip Hazel
+        University Computing Service
+        Cambridge CB2 3QH, England.
-      int pcre_info(const pcre *code, int *optptr, *firstcharptr);
+        Putting an actual email address here seems to have been a spam  magnet,
+        so  I've  taken  it away. If you want to email me, use my two initials,
+        followed by the two digits 10, at the domain cam.ac.uk.
-      char *pcre_version(void);
-      void *(*pcre_malloc)(size_t);
+ REVISION
-      void (*pcre_free)(void *);
+        Last updated: 18 April 2007
+        Copyright (c) 1997-2007 University of Cambridge.
+ ------------------------------------------------------------------------------
+ PCREBUILD(3)                                                      PCREBUILD(3)
- DESCRIPTION
+ NAME
-      The PCRE library is a set of functions that implement  regu-
+        PCRE - Perl-compatible regular expressions
-      lar  expression  pattern  matching using the same syntax and
-      semantics as Perl  5,  with  just  a  few  differences  (see
-      below).  The  current  implementation  corresponds  to  Perl
+ PCRE BUILD-TIME OPTIONS
-.005.
+        This  document  describes  the  optional  features  of PCRE that can be
-      PCRE has its own native API,  which  is  described  in  this
+        selected when the library is compiled. They are all selected, or  dese-
-      document.  There  is  also  a  set of wrapper functions that
+        lected, by providing options to the configure script that is run before
-      correspond to the POSIX API.  These  are  described  in  the
+        the make command. The complete list of  options  for  configure  (which
-      pcreposix documentation.
+        includes  the  standard  ones such as the selection of the installation
-      The native API function prototypes are defined in the header
+        directory) can be obtained by running
-      file  pcre.h,  and  on  Unix  systems  the library itself is
-      called libpcre.a, so can be accessed by adding -lpcre to the
+          ./configure --help
-      command for linking an application which calls it.
+        The following sections include  descriptions  of  options  whose  names
-      The functions pcre_compile(), pcre_study(), and  pcre_exec()
+        begin with --enable or --disable. These settings specify changes to the
-      are  used  for  compiling  and matching regular expressions,
+        defaults for the configure command. Because of the way  that  configure
-      while   pcre_copy_substring(),   pcre_get_substring(),   and
+        works,  --enable  and --disable always come in pairs, so the complemen-
-      pcre_get_substring_list()   are  convenience  functions  for
+        tary option always exists as well, but as it specifies the default,  it
-      extracting  captured  substrings  from  a  matched   subject
+        is not described.
-      string.  The function pcre_maketables() is used (optionally)
-      to build a set of character tables in the current locale for
-      passing to pcre_compile().
+ C++ SUPPORT
-      The function pcre_info() is used  to  find  out  information
+        By default, the configure script will search for a C++ compiler and C++
-      about  a compiled pattern, while the function pcre_version()
+        header files. If it finds them, it automatically builds the C++ wrapper
-      returns a pointer to a string containing the version of PCRE
+        library for PCRE. You can disable this by adding
-      and its date of release.
+          --disable-cpp
-      The global variables  pcre_malloc  and  pcre_free  initially
-      contain the entry points of the standard malloc() and free()
+        to the configure command.
-      functions respectively. PCRE  calls  the  memory  management
-      functions  via  these  variables,  so  a calling program can
-      replace them if it  wishes  to  intercept  the  calls.  This
+ UTF-8 SUPPORT
-      should be done before calling any PCRE functions.
+        To build PCRE with support for UTF-8 character strings, add
+          --enable-utf8
+        to  the  configure  command.  Of  itself, this does not make PCRE treat
+        strings as UTF-8. As well as compiling PCRE with this option, you  also
+        have  have to set the PCRE_UTF8 option when you call the pcre_compile()
+        function.
+ UNICODE CHARACTER PROPERTY SUPPORT
+        UTF-8 support allows PCRE to process character values greater than  255
+        in  the  strings that it handles. On its own, however, it does not pro-
+        vide any facilities for accessing the properties of such characters. If
+        you  want  to  be able to use the pattern escapes \P, \p, and \X, which
+        refer to Unicode character properties, you must add
+          --enable-unicode-properties
+        to the configure command. This implies UTF-8 support, even if you  have
+        not explicitly requested it.
+        Including  Unicode  property  support  adds around 30K of tables to the
+        PCRE library. Only the general category properties such as  Lu  and  Nd
+        are supported. Details are given in the pcrepattern documentation.
+ CODE VALUE OF NEWLINE
+        By  default,  PCRE interprets character 10 (linefeed, LF) as indicating
+        the end of a line. This is the normal newline  character  on  Unix-like
+        systems. You can compile PCRE to use character 13 (carriage return, CR)
+        instead, by adding
+          --enable-newline-is-cr
+        to the  configure  command.  There  is  also  a  --enable-newline-is-lf
+        option, which explicitly specifies linefeed as the newline character.
+        Alternatively, you can specify that line endings are to be indicated by
+        the two character sequence CRLF. If you want this, add
+          --enable-newline-is-crlf
+        to the configure command. There is a fourth option, specified by
+          --enable-newline-is-anycrlf
+        which causes PCRE to recognize any of the three sequences  CR,  LF,  or
+        CRLF as indicating a line ending. Finally, a fifth option, specified by
+          --enable-newline-is-any
+        causes PCRE to recognize any Unicode newline sequence.
+        Whatever line ending convention is selected when PCRE is built  can  be
+        overridden  when  the library functions are called. At build time it is
+        conventional to use the standard for your operating system.
+ BUILDING SHARED AND STATIC LIBRARIES
+        The PCRE building process uses libtool to build both shared and  static
+        Unix  libraries by default. You can suppress one of these by adding one
+        of
+          --disable-shared
+          --disable-static
+        to the configure command, as required.
+ POSIX MALLOC USAGE
+        When PCRE is called through the POSIX interface (see the pcreposix doc-
+        umentation),  additional  working  storage  is required for holding the
+        pointers to capturing substrings, because PCRE requires three  integers
+        per  substring,  whereas  the POSIX interface provides only two. If the
+        number of expected substrings is small, the wrapper function uses space
+        on the stack, because this is faster than using malloc() for each call.
+        The default threshold above which the stack is no longer used is 10; it
+        can be changed by adding a setting such as
+          --with-posix-malloc-threshold=20
+        to the configure command.
+ HANDLING VERY LARGE PATTERNS
+        Within  a  compiled  pattern,  offset values are used to point from one
+        part to another (for example, from an opening parenthesis to an  alter-
+        nation  metacharacter).  By default, two-byte values are used for these
+        offsets, leading to a maximum size for a  compiled  pattern  of  around
+K.  This  is sufficient to handle all but the most gigantic patterns.
+        Nevertheless, some people do want to process enormous patterns,  so  it
+        is  possible  to compile PCRE to use three-byte or four-byte offsets by
+        adding a setting such as
+          --with-link-size=3
+        to the configure command. The value given must be 2,  3,  or  4.  Using
+        longer  offsets slows down the operation of PCRE because it has to load
+        additional bytes when handling them.
+ AVOIDING EXCESSIVE STACK USAGE
+        When matching with the pcre_exec() function, PCRE implements backtrack-
+        ing  by  making recursive calls to an internal function called match().
+        In environments where the size of the stack is limited,  this  can  se-
+        verely  limit  PCRE's operation. (The Unix environment does not usually
+        suffer from this problem, but it may sometimes be necessary to increase
+        the  maximum  stack size.  There is a discussion in the pcrestack docu-
+        mentation.) An alternative approach to recursion that uses memory  from
+        the  heap  to remember data, instead of using recursive function calls,
+        has been implemented to work round the problem of limited  stack  size.
+        If you want to build a version of PCRE that works this way, add
+          --disable-stack-for-recursion
+        to  the  configure  command. With this configuration, PCRE will use the
+        pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
+        ment  functions.  Separate  functions are provided because the usage is
+        very predictable: the block sizes requested are always  the  same,  and
+        the  blocks  are always freed in reverse order. A calling program might
+        be able to implement optimized functions that perform better  than  the
+        standard  malloc()  and  free()  functions.  PCRE  runs noticeably more
+        slowly when built in this way. This option affects only the pcre_exec()
+        function; it is not relevant for the the pcre_dfa_exec() function.
+ LIMITING PCRE RESOURCE USAGE
+        Internally,  PCRE has a function called match(), which it calls repeat-
+        edly  (sometimes  recursively)  when  matching  a  pattern   with   the
+        pcre_exec()  function.  By controlling the maximum number of times this
+        function may be called during a single matching operation, a limit  can
+        be  placed  on  the resources used by a single call to pcre_exec(). The
+        limit can be changed at run time, as described in the pcreapi  documen-
+        tation.  The default is 10 million, but this can be changed by adding a
+        setting such as
+          --with-match-limit=500000
+        to  the  configure  command.  This  setting  has  no  effect   on   the
+        pcre_dfa_exec() matching function.
+        In  some  environments  it is desirable to limit the depth of recursive
+        calls of match() more strictly than the total number of calls, in order
+        to  restrict  the maximum amount of stack (or heap, if --disable-stack-
+        for-recursion is specified) that is used. A second limit controls this;
+        it  defaults  to  the  value  that is set for --with-match-limit, which
+        imposes no additional constraints. However, you can set a  lower  limit
+        by adding, for example,
+          --with-match-limit-recursion=10000
+        to  the  configure  command.  This  value can also be overridden at run
+        time.
+ CREATING CHARACTER TABLES AT BUILD TIME
+        PCRE uses fixed tables for processing characters whose code values  are
+        less  than 256. By default, PCRE is built with a set of tables that are
+        distributed in the file pcre_chartables.c.dist. These  tables  are  for
+        ASCII codes only. If you add
+          --enable-rebuild-chartables
+        to  the  configure  command, the distributed tables are no longer used.
+        Instead, a program called dftables is compiled and  run.  This  outputs
+        the source for new set of tables, created in the default locale of your
+        C runtime system. (This method of replacing the tables does not work if
+        you  are cross compiling, because dftables is run on the local host. If
+        you need to create alternative tables when cross  compiling,  you  will
+        have to do so "by hand".)
+ USING EBCDIC CODE
+        PCRE  assumes  by  default that it will run in an environment where the
+        character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
+        PCRE  can,  however,  be  compiled  to  run in an EBCDIC environment by
+        adding
+          --enable-ebcdic
+        to the configure command. This setting implies --enable-rebuild-charta-
+        bles.
+ SEE ALSO
+        pcreapi(3), pcre_config(3).
+ AUTHOR
+        Philip Hazel
+        University Computing Service
+        Cambridge CB2 3QH, England.
+ REVISION
+        Last updated: 16 April 2007
+        Copyright (c) 1997-2007 University of Cambridge.
+ ------------------------------------------------------------------------------
+ PCREMATCHING(3)                                                PCREMATCHING(3)
+ NAME
+        PCRE - Perl-compatible regular expressions
+ PCRE MATCHING ALGORITHMS
+        This document describes the two different algorithms that are available
+        in PCRE for matching a compiled regular expression against a given sub-
+        ject  string.  The  "standard"  algorithm  is  the  one provided by the
+        pcre_exec() function.  This works in the same was  as  Perl's  matching
+        function, and provides a Perl-compatible matching operation.
+        An  alternative  algorithm is provided by the pcre_dfa_exec() function;
+        this operates in a different way, and is not  Perl-compatible.  It  has
+        advantages  and disadvantages compared with the standard algorithm, and
+        these are described below.
+        When there is only one possible way in which a given subject string can
+        match  a pattern, the two algorithms give the same answer. A difference
+        arises, however, when there are multiple possibilities. For example, if
+        the pattern
+          ^<.*>
+        is matched against the string
+          <something> <something else> <something further>
+        there are three possible answers. The standard algorithm finds only one
+        of them, whereas the alternative algorithm finds all three.
+ REGULAR EXPRESSIONS AS TREES
+        The set of strings that are matched by a regular expression can be rep-
+        resented  as  a  tree structure. An unlimited repetition in the pattern
+        makes the tree of infinite size, but it is still a tree.  Matching  the
+        pattern  to a given subject string (from a given starting point) can be
+        thought of as a search of the tree.  There are two  ways  to  search  a
+        tree:  depth-first  and  breadth-first, and these correspond to the two
+        matching algorithms provided by PCRE.
+ THE STANDARD MATCHING ALGORITHM
+        In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
+        sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
+        depth-first search of the pattern tree. That is, it  proceeds  along  a
+        single path through the tree, checking that the subject matches what is
+        required. When there is a mismatch, the algorithm  tries  any  alterna-
+        tives  at  the  current point, and if they all fail, it backs up to the
+        previous branch point in the  tree,  and  tries  the  next  alternative
+        branch  at  that  level.  This often involves backing up (moving to the
+        left) in the subject string as well.  The  order  in  which  repetition
+        branches  are  tried  is controlled by the greedy or ungreedy nature of
+        the quantifier.
+        If a leaf node is reached, a matching string has  been  found,  and  at
+        that  point the algorithm stops. Thus, if there is more than one possi-
+        ble match, this algorithm returns the first one that it finds.  Whether
+        this  is the shortest, the longest, or some intermediate length depends
+        on the way the greedy and ungreedy repetition quantifiers are specified
+        in the pattern.
+        Because  it  ends  up  with a single path through the tree, it is rela-
+        tively straightforward for this algorithm to keep  track  of  the  sub-
+        strings  that  are  matched  by portions of the pattern in parentheses.
+        This provides support for capturing parentheses and back references.
+ THE ALTERNATIVE MATCHING ALGORITHM
+        This algorithm conducts a breadth-first search of  the  tree.  Starting
+        from  the  first  matching  point  in the subject, it scans the subject
+        string from left to right, once, character by character, and as it does
+        this,  it remembers all the paths through the tree that represent valid
+        matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
+        though  it is not implemented as a traditional finite state machine (it
+        keeps multiple states active simultaneously).
+        The scan continues until either the end of the subject is  reached,  or
+        there  are  no more unterminated paths. At this point, terminated paths
+        represent the different matching possibilities (if there are none,  the
+        match  has  failed).   Thus,  if there is more than one possible match,
+        this algorithm finds all of them, and in particular, it finds the long-
+        est.  In PCRE, there is an option to stop the algorithm after the first
+        match (which is necessarily the shortest) has been found.
+        Note that all the matches that are found start at the same point in the
+        subject. If the pattern
+          cat(er(pillar)?)
+        is  matched  against the string "the caterpillar catchment", the result
+        will be the three strings "cat", "cater", and "caterpillar" that  start
+        at the fourth character of the subject. The algorithm does not automat-
+        ically move on to find matches that start at later positions.
+        There are a number of features of PCRE regular expressions that are not
+        supported by the alternative matching algorithm. They are as follows:
+.  Because  the  algorithm  finds  all possible matches, the greedy or
+        ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
+        ungreedy quantifiers are treated in exactly the same way. However, pos-
+        sessive quantifiers can make a difference when what follows could  also
+        match what is quantified, for example in a pattern like this:
+          ^a++\w!
+        This  pattern matches "aaab!" but not "aaa!", which would be matched by
+        a non-possessive quantifier. Similarly, if an atomic group is  present,
+        it  is matched as if it were a standalone pattern at the current point,
+        and the longest match is then "locked in" for the rest of  the  overall
+        pattern.
+. When dealing with multiple paths through the tree simultaneously, it
+        is not straightforward to keep track of  captured  substrings  for  the
+        different  matching  possibilities,  and  PCRE's implementation of this
+        algorithm does not attempt to do this. This means that no captured sub-
+        strings are available.
+.  Because no substrings are captured, back references within the pat-
+        tern are not supported, and cause errors if encountered.
+. For the same reason, conditional expressions that use  a  backrefer-
+        ence  as  the  condition or test for a specific group recursion are not
+        supported.
+. Callouts are supported, but the value of the  capture_top  field  is
+        always 1, and the value of the capture_last field is always -1.
+.  The \C escape sequence, which (in the standard algorithm) matches a
+        single byte, even in UTF-8 mode, is not supported because the  alterna-
+        tive  algorithm  moves  through  the  subject string one character at a
+        time, for all active paths through the tree.
- MULTI-THREADING
+ ADVANTAGES OF THE ALTERNATIVE ALGORITHM
-      The PCRE functions can be used in  multi-threading  applica-
-      tions, with the proviso that the memory management functions
-      pointed to by pcre_malloc and pcre_free are  shared  by  all
-      threads.
-      The compiled form of a regular  expression  is  not  altered
-      during  matching, so the same compiled pattern can safely be
-      used by several threads at once.
+        Using the alternative matching algorithm provides the following  advan-
+        tages:
+. All possible matches (at a single point in the subject) are automat-
+        ically found, and in particular, the longest match is  found.  To  find
+        more than one match using the standard algorithm, you have to do kludgy
+        things with callouts.
+. There is much better support for partial matching. The  restrictions
+        on  the content of the pattern that apply when using the standard algo-
+        rithm for partial matching do not apply to the  alternative  algorithm.
+        For  non-anchored patterns, the starting position of a partial match is
+        available.
+. Because the alternative algorithm  scans  the  subject  string  just
+        once,  and  never  needs to backtrack, it is possible to pass very long
+        subject strings to the matching function in  several  pieces,  checking
+        for partial matching each time.
+ DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
+        The alternative algorithm suffers from a number of disadvantages:
+.  It  is  substantially  slower  than the standard algorithm. This is
+        partly because it has to search for all possible matches, but  is  also
+        because it is less susceptible to optimization.
+. Capturing parentheses and back references are not supported.
+. Although atomic groups are supported, their use does not provide the
+        performance advantage that it does for the standard algorithm.
+ AUTHOR
+        Philip Hazel
+        University Computing Service
+        Cambridge CB2 3QH, England.
+ REVISION
+        Last updated: 06 March 2007
+        Copyright (c) 1997-2007 University of Cambridge.
+ ------------------------------------------------------------------------------
+ PCREAPI(3)                                                          PCREAPI(3)
+ NAME
+        PCRE - Perl-compatible regular expressions
+ PCRE NATIVE API
+        #include <pcre.h>
+        pcre *pcre_compile(const char *pattern, int options,
+             const char **errptr, int *erroffset,
+             const unsigned char *tableptr);
+        pcre *pcre_compile2(const char *pattern, int options,
+             int *errorcodeptr,
+             const char **errptr, int *erroffset,
+             const unsigned char *tableptr);
+        pcre_extra *pcre_study(const pcre *code, int options,
+             const char **errptr);
+        int pcre_exec(const pcre *code, const pcre_extra *extra,
+             const char *subject, int length, int startoffset,
+             int options, int *ovector, int ovecsize);
+        int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
+             const char *subject, int length, int startoffset,
+             int options, int *ovector, int ovecsize,
+             int *workspace, int wscount);
+        int pcre_copy_named_substring(const pcre *code,
+             const char *subject, int *ovector,
+             int stringcount, const char *stringname,
+             char *buffer, int buffersize);
+        int pcre_copy_substring(const char *subject, int *ovector,
+             int stringcount, int stringnumber, char *buffer,
+             int buffersize);
+        int pcre_get_named_substring(const pcre *code,
+             const char *subject, int *ovector,
+             int stringcount, const char *stringname,
+             const char **stringptr);
+        int pcre_get_stringnumber(const pcre *code,
+             const char *name);
+        int pcre_get_stringtable_entries(const pcre *code,
+             const char *name, char **first, char **last);
+        int pcre_get_substring(const char *subject, int *ovector,
+             int stringcount, int stringnumber,
+             const char **stringptr);
+        int pcre_get_substring_list(const char *subject,
+             int *ovector, int stringcount, const char ***listptr);
+        void pcre_free_substring(const char *stringptr);
+        void pcre_free_substring_list(const char **stringptr);
+        const unsigned char *pcre_maketables(void);
+        int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
+             int what, void *where);
+        int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
+        int pcre_refcount(pcre *code, int adjust);
+        int pcre_config(int what, void *where);
+        char *pcre_version(void);
+        void *(*pcre_malloc)(size_t);
+        void (*pcre_free)(void *);
+        void *(*pcre_stack_malloc)(size_t);
+        void (*pcre_stack_free)(void *);
+        int (*pcre_callout)(pcre_callout_block *);
+ PCRE API OVERVIEW
+        PCRE has its own native API, which is described in this document. There
+        are also some wrapper functions that correspond to  the  POSIX  regular
+        expression  API.  These  are  described in the pcreposix documentation.
+        Both of these APIs define a set of C function calls. A C++  wrapper  is
+        distributed with PCRE. It is documented in the pcrecpp page.
+        The  native  API  C  function prototypes are defined in the header file
+        pcre.h, and on Unix systems the library itself is called  libpcre.   It
+        can normally be accessed by adding -lpcre to the command for linking an
+        application  that  uses  PCRE.  The  header  file  defines  the  macros
+        PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
+        bers for the library.  Applications can use these  to  include  support
+        for different releases of PCRE.
+        The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
+        pcre_exec() are used for compiling and matching regular expressions  in
+        a  Perl-compatible  manner. A sample program that demonstrates the sim-
+        plest way of using them is provided in the file  called  pcredemo.c  in
+        the  source distribution. The pcresample documentation describes how to
+        run it.
+        A second matching function, pcre_dfa_exec(), which is not Perl-compati-
+        ble,  is  also provided. This uses a different algorithm for the match-
+        ing. The alternative algorithm finds all possible matches (at  a  given
+        point  in  the subject), and scans the subject just once. However, this
+        algorithm does not return captured substrings. A description of the two
+        matching  algorithms and their advantages and disadvantages is given in
+        the pcrematching documentation.
+        In addition to the main compiling and  matching  functions,  there  are
+        convenience functions for extracting captured substrings from a subject
+        string that is matched by pcre_exec(). They are:
+          pcre_copy_substring()
+          pcre_copy_named_substring()
+          pcre_get_substring()
+          pcre_get_named_substring()
+          pcre_get_substring_list()
+          pcre_get_stringnumber()
+          pcre_get_stringtable_entries()
+        pcre_free_substring() and pcre_free_substring_list() are also provided,
+        to free the memory used for extracted strings.
+        The  function  pcre_maketables()  is  used  to build a set of character
+        tables  in  the  current  locale   for   passing   to   pcre_compile(),
+        pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
+        provided for specialist use.  Most  commonly,  no  special  tables  are
+        passed,  in  which case internal tables that are generated when PCRE is
+        built are used.
+        The function pcre_fullinfo() is used to find out  information  about  a
+        compiled  pattern; pcre_info() is an obsolete version that returns only
+        some of the available information, but is retained for  backwards  com-
+        patibility.   The function pcre_version() returns a pointer to a string
+        containing the version of PCRE and its date of release.
+        The function pcre_refcount() maintains a  reference  count  in  a  data
+        block  containing  a compiled pattern. This is provided for the benefit
+        of object-oriented applications.
+        The global variables pcre_malloc and pcre_free  initially  contain  the
+        entry  points  of  the  standard malloc() and free() functions, respec-
+        tively. PCRE calls the memory management functions via these variables,
+        so  a  calling  program  can replace them if it wishes to intercept the
+        calls. This should be done before calling any PCRE functions.
+        The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
+        indirections  to  memory  management functions. These special functions
+        are used only when PCRE is compiled to use  the  heap  for  remembering
+        data, instead of recursive function calls, when running the pcre_exec()
+        function. See the pcrebuild documentation for  details  of  how  to  do
+        this.  It  is  a non-standard way of building PCRE, for use in environ-
+        ments that have limited stacks. Because of the greater  use  of  memory
+        management,  it  runs  more  slowly. Separate functions are provided so
+        that special-purpose external code can be  used  for  this  case.  When
+        used,  these  functions  are always called in a stack-like manner (last
+        obtained, first freed), and always for memory blocks of the same  size.
+        There  is  a discussion about PCRE's stack usage in the pcrestack docu-
+        mentation.
+        The global variable pcre_callout initially contains NULL. It can be set
+        by  the  caller  to  a "callout" function, which PCRE will then call at
+        specified points during a matching operation. Details are given in  the
+        pcrecallout documentation.
+ NEWLINES
+        PCRE  supports five different conventions for indicating line breaks in
+        strings: a single CR (carriage return) character, a  single  LF  (line-
+        feed) character, the two-character sequence CRLF, any of the three pre-
+        ceding, or any Unicode newline sequence. The Unicode newline  sequences
+        are  the  three just mentioned, plus the single characters VT (vertical
+        tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
+        separator, U+2028), and PS (paragraph separator, U+2029).
+        Each  of  the first three conventions is used by at least one operating
+        system as its standard newline sequence. When PCRE is built, a  default
+        can  be  specified.  The default default is LF, which is the Unix stan-
+        dard. When PCRE is run, the default can be overridden,  either  when  a
+        pattern is compiled, or when it is matched.
+        In the PCRE documentation the word "newline" is used to mean "the char-
+        acter or pair of characters that indicate a line break". The choice  of
+        newline  convention  affects  the  handling of the dot, circumflex, and
+        dollar metacharacters, the handling of #-comments in /x mode, and, when
+        CRLF  is a recognized line ending sequence, the match position advance-
+        ment for a non-anchored pattern. The choice of newline convention  does
+        not affect the interpretation of the \n or \r escape sequences.
+ MULTITHREADING
+        The  PCRE  functions  can be used in multi-threading applications, with
+        the  proviso  that  the  memory  management  functions  pointed  to  by
+        pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
+        callout function pointed to by pcre_callout, are shared by all threads.
+        The  compiled form of a regular expression is not altered during match-
+        ing, so the same compiled pattern can safely be used by several threads
+        at once.
+ SAVING PRECOMPILED PATTERNS FOR LATER USE
+        The compiled form of a regular expression can be saved and re-used at a
+        later time, possibly by a different program, and even on a  host  other
+        than  the  one  on  which  it  was  compiled.  Details are given in the
+        pcreprecompile documentation. However, compiling a  regular  expression
+        with  one version of PCRE for use with a different version is not guar-
+        anteed to work and may cause crashes.
+ CHECKING BUILD-TIME OPTIONS
+        int pcre_config(int what, void *where);
+        The function pcre_config() makes it possible for a PCRE client to  dis-
+        cover which optional features have been compiled into the PCRE library.
+        The pcrebuild documentation has more details about these optional  fea-
+        tures.
+        The  first  argument  for pcre_config() is an integer, specifying which
+        information is required; the second argument is a pointer to a variable
+        into  which  the  information  is  placed. The following information is
+        available:
+          PCRE_CONFIG_UTF8
+        The output is an integer that is set to one if UTF-8 support is  avail-
+        able; otherwise it is set to zero.
+          PCRE_CONFIG_UNICODE_PROPERTIES
+        The  output  is  an  integer  that is set to one if support for Unicode
+        character properties is available; otherwise it is set to zero.
+          PCRE_CONFIG_NEWLINE
+        The output is an integer whose value specifies  the  default  character
+        sequence  that is recognized as meaning "newline". The four values that
+        are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
+        and  -1  for  ANY. The default should normally be the standard sequence
+        for your operating system.
+          PCRE_CONFIG_LINK_SIZE
+        The output is an integer that contains the number  of  bytes  used  for
+        internal linkage in compiled regular expressions. The value is 2, 3, or
+. Larger values allow larger regular expressions to  be  compiled,  at
+        the  expense  of  slower matching. The default value of 2 is sufficient
+        for all but the most massive patterns, since  it  allows  the  compiled
+        pattern to be up to 64K in size.
+          PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
+        The  output  is  an integer that contains the threshold above which the
+        POSIX interface uses malloc() for output vectors. Further  details  are
+        given in the pcreposix documentation.
+          PCRE_CONFIG_MATCH_LIMIT
+        The output is an integer that gives the default limit for the number of
+        internal matching function calls in a  pcre_exec()  execution.  Further
+        details are given with pcre_exec() below.
+          PCRE_CONFIG_MATCH_LIMIT_RECURSION
+        The  output is an integer that gives the default limit for the depth of
+        recursion when calling the internal matching function in a  pcre_exec()
+        execution. Further details are given with pcre_exec() below.
+          PCRE_CONFIG_STACKRECURSE
+        The  output is an integer that is set to one if internal recursion when
+        running pcre_exec() is implemented by recursive function calls that use
+        the  stack  to remember their state. This is the usual way that PCRE is
+        compiled. The output is zero if PCRE was compiled to use blocks of data
+        on  the  heap  instead  of  recursive  function  calls.  In  this case,
+        pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
+        blocks on the heap, thus avoiding the use of the stack.
  COMPILING A PATTERN
-      The function pcre_compile() is called to compile  a  pattern
-      into  an internal form. The pattern is a C string terminated
-      by a binary zero, and is passed in the argument  pattern.  A
-      pointer  to  a  single  block of memory that is obtained via
-      pcre_malloc is returned. This contains the compiled code and
-      related data. The pcre type is defined for this for conveni-
-      ence, but in fact pcre is just a typedef for void, since the
-      contents  of  the block are not externally defined. It is up
-      to the caller to free  the  memory  when  it  is  no  longer
-      required.
-      The size of a compiled pattern is  roughly  proportional  to
-      the length of the pattern string, except that each character
-      class (other than those containing just a single  character,
-      negated  or  not)  requires 33 bytes, and repeat quantifiers
-      with a minimum greater than one or a bounded  maximum  cause
-      the  relevant  portions of the compiled pattern to be repli-
-      cated.
-      The options argument contains independent bits  that  affect
-      the  compilation.  It  should  be  zero  if  no  options are
-      required. Some of the options, in particular, those that are
-      compatible  with Perl, can also be set and unset from within
-      the pattern (see the detailed description of regular expres-
-      sions below). For these options, the contents of the options
-      argument specifies their initial settings at  the  start  of
-      compilation  and  execution. The PCRE_ANCHORED option can be
-      set at the time of matching as well as at compile time.
-      If errptr is NULL, pcre_compile() returns NULL  immediately.
-      Otherwise, if compilation of a pattern fails, pcre_compile()
-      returns NULL, and sets the variable pointed to by errptr  to
-      point  to a textual error message. The offset from the start
-      of  the  pattern  to  the  character  where  the  error  was
-      discovered   is   placed  in  the  variable  pointed  to  by
-      erroffset, which must not be NULL. If it  is,  an  immediate
-      error is given.
-      If the final  argument,  tableptr,  is  NULL,  PCRE  uses  a
-      default  set  of character tables which are built when it is
-      compiled, using the default C  locale.  Otherwise,  tableptr
-      must  be  the result of a call to pcre_maketables(). See the
-      section on locale support below.
-      The following option bits are defined in the header file:
-        PCRE_ANCHORED
-      If this bit is set, the pattern is forced to be  "anchored",
-      that is, it is constrained to match only at the start of the
-      string which is being searched (the "subject string").  This
-      effect can also be achieved by appropriate constructs in the
-      pattern itself, which is the only way to do it in Perl.
-        PCRE_CASELESS
-      If this bit is set, letters in the pattern match both  upper
-      and  lower  case  letters.  It  is  equivalent  to Perl's /i
-      option.
-        PCRE_DOLLAR_ENDONLY
-      If this bit is set, a dollar metacharacter  in  the  pattern
-      matches  only at the end of the subject string. Without this
-      option, a dollar also matches immediately before  the  final
-      character  if it is a newline (but not before any other new-
-      lines).  The  PCRE_DOLLAR_ENDONLY  option  is   ignored   if
-      PCRE_MULTILINE is set. There is no equivalent to this option
-      in Perl.
-        PCRE_DOTALL
-      If this bit is  set,  a  dot  metacharater  in  the  pattern
-      matches all characters, including newlines. Without it, new-
-      lines are excluded. This option is equivalent to  Perl's  /s
-      option.  A negative class such as [^a] always matches a new-
-      line character, independent of the setting of this option.
-        PCRE_EXTENDED
-      If this bit is set, whitespace data characters in  the  pat-
-      tern  are  totally  ignored  except when escaped or inside a
-      character class, and characters between an unescaped #  out-
-      side  a  character  class  and  the  next newline character,
-      inclusive, are also ignored. This is equivalent to Perl's /x
-      option,  and  makes  it  possible to include comments inside
-      complicated patterns. Note, however, that this applies  only
-      to  data  characters. Whitespace characters may never appear
-      within special character sequences in a pattern, for example
-      within  the sequence (?( which introduces a conditional sub-
-      pattern.
-        PCRE_EXTRA
-      This option turns on additional functionality of  PCRE  that
-      is  incompatible  with Perl. Any backslash in a pattern that
-      is followed by a letter that has no special  meaning  causes
-      an  error,  thus  reserving  these  combinations  for future
-      expansion. By default, as in Perl, a backslash followed by a
-      letter  with  no  special  meaning  is treated as a literal.
-      There are at present no other features  controlled  by  this
-      option.
-        PCRE_MULTILINE
-      By default, PCRE treats the subject string as consisting  of
-      a  single "line" of characters (even if it actually contains
-      several newlines). The "start  of  line"  metacharacter  (^)
-      matches  only  at the start of the string, while the "end of
-      line" metacharacter ($) matches  only  at  the  end  of  the
-      string,    or   before   a   terminating   newline   (unless
-      PCRE_DOLLAR_ENDONLY is set). This is the same as Perl.
-      When PCRE_MULTILINE it is set, the "start of line" and  "end
-      of   line"   constructs   match   immediately  following  or
-      immediately  before  any  newline  in  the  subject  string,
-      respectively,  as well as at the very start and end. This is
-      equivalent to Perl's /m option. If there are no "\n" charac-
-      ters  in  a subject string, or no occurrences of ^ or $ in a
-      pattern, setting PCRE_MULTILINE has no effect.
-        PCRE_UNGREEDY
-      This option inverts the "greediness" of the  quantifiers  so
-      that  they  are  not greedy by default, but become greedy if
-      followed by "?". It is not compatible with Perl. It can also
-      be set by a (?U) option setting within the pattern.
+        pcre *pcre_compile(const char *pattern, int options,
+             const char **errptr, int *erroffset,
+             const unsigned char *tableptr);
+        pcre *pcre_compile2(const char *pattern, int options,
+             int *errorcodeptr,
+             const char **errptr, int *erroffset,
+             const unsigned char *tableptr);
+        Either of the functions pcre_compile() or pcre_compile2() can be called
+        to compile a pattern into an internal form. The only difference between
+        the  two interfaces is that pcre_compile2() has an additional argument,
+        errorcodeptr, via which a numerical error code can be returned.
+        The pattern is a C string terminated by a binary zero, and is passed in
+        the  pattern  argument.  A  pointer to a single block of memory that is
+        obtained via pcre_malloc is returned. This contains the  compiled  code
+        and related data. The pcre type is defined for the returned block; this
+        is a typedef for a structure whose contents are not externally defined.
+        It is up to the caller to free the memory (via pcre_free) when it is no
+        longer required.
+        Although the compiled code of a PCRE regex is relocatable, that is,  it
+        does not depend on memory location, the complete pcre data block is not
+        fully relocatable, because it may contain a copy of the tableptr  argu-
+        ment, which is an address (see below).
+        The options argument contains various bit settings that affect the com-
+        pilation. It should be zero if no options are required.  The  available
+        options  are  described  below. Some of them, in particular, those that
+        are compatible with Perl, can also be set and  unset  from  within  the
+        pattern  (see  the  detailed  description in the pcrepattern documenta-
+        tion). For these options, the contents of the options  argument  speci-
+        fies  their initial settings at the start of compilation and execution.
+        The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at  the  time
+        of matching as well as at compile time.
+        If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
+        if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
+        sets the variable pointed to by errptr to point to a textual error mes-
+        sage. This is a static string that is part of the library. You must not
+        try to free it. The offset from the start of the pattern to the charac-
+        ter where the error was discovered is placed in the variable pointed to
+        by  erroffset,  which must not be NULL. If it is, an immediate error is
+        given.
+        If pcre_compile2() is used instead of pcre_compile(),  and  the  error-
+        codeptr  argument is not NULL, a non-zero error code number is returned
+        via this argument in the event of an error. This is in addition to  the
+        textual error message. Error codes and messages are listed below.
+        If  the  final  argument, tableptr, is NULL, PCRE uses a default set of
+        character tables that are  built  when  PCRE  is  compiled,  using  the
+        default  C  locale.  Otherwise, tableptr must be an address that is the
+        result of a call to pcre_maketables(). This value is  stored  with  the
+        compiled  pattern,  and used again by pcre_exec(), unless another table
+        pointer is passed to it. For more discussion, see the section on locale
+        support below.
+        This  code  fragment  shows a typical straightforward call to pcre_com-
+        pile():
+          pcre *re;
+          const char *error;
+          int erroffset;
+          re = pcre_compile(
+            "^A.*Z",          /* the pattern */
+,                /* default options */
+            &error,           /* for error message */
+            &erroffset,       /* for error offset */
+            NULL);            /* use default character tables */
+        The following names for option bits are defined in  the  pcre.h  header
+        file:
+          PCRE_ANCHORED
+        If this bit is set, the pattern is forced to be "anchored", that is, it
+        is constrained to match only at the first matching point in the  string
+        that  is being searched (the "subject string"). This effect can also be
+        achieved by appropriate constructs in the pattern itself, which is  the
+        only way to do it in Perl.
+          PCRE_AUTO_CALLOUT
+        If this bit is set, pcre_compile() automatically inserts callout items,
+        all with number 255, before each pattern item. For  discussion  of  the
+        callout facility, see the pcrecallout documentation.
+          PCRE_CASELESS
+        If  this  bit is set, letters in the pattern match both upper and lower
+        case letters. It is equivalent to Perl's  /i  option,  and  it  can  be
+        changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
+        always understands the concept of case for characters whose values  are
+        less  than 128, so caseless matching is always possible. For characters
+        with higher values, the concept of case is supported if  PCRE  is  com-
+        piled  with Unicode property support, but not otherwise. If you want to
+        use caseless matching for characters 128 and  above,  you  must  ensure
+        that  PCRE  is  compiled  with Unicode property support as well as with
+        UTF-8 support.
+          PCRE_DOLLAR_ENDONLY
+        If this bit is set, a dollar metacharacter in the pattern matches  only
+        at  the  end  of the subject string. Without this option, a dollar also
+        matches immediately before a newline at the end of the string (but  not
+        before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
+        if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in
+        Perl, and no way to set it within a pattern.
+          PCRE_DOTALL
+        If this bit is set, a dot metacharater in the pattern matches all char-
+        acters, including those that indicate newline. Without it, a  dot  does
+        not  match  when  the  current position is at a newline. This option is
+        equivalent to Perl's /s option, and it can be changed within a  pattern
+        by  a (?s) option setting. A negative class such as [^a] always matches
+        newline characters, independent of the setting of this option.
+          PCRE_DUPNAMES
+        If this bit is set, names used to identify capturing  subpatterns  need
+        not be unique. This can be helpful for certain types of pattern when it
+        is known that only one instance of the named  subpattern  can  ever  be
+        matched.  There  are  more details of named subpatterns below; see also
+        the pcrepattern documentation.
+          PCRE_EXTENDED
+        If this bit is set, whitespace  data  characters  in  the  pattern  are
+        totally ignored except when escaped or inside a character class. White-
+        space does not include the VT character (code 11). In addition, charac-
+        ters between an unescaped # outside a character class and the next new-
+        line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
+        option,  and  it  can be changed within a pattern by a (?x) option set-
+        ting.
+        This option makes it possible to include  comments  inside  complicated
+        patterns.   Note,  however,  that this applies only to data characters.
+        Whitespace  characters  may  never  appear  within  special   character
+        sequences  in  a  pattern,  for  example  within the sequence (?( which
+        introduces a conditional subpattern.
+          PCRE_EXTRA
+        This option was invented in order to turn on  additional  functionality
+        of  PCRE  that  is  incompatible with Perl, but it is currently of very
+        little use. When set, any backslash in a pattern that is followed by  a
+        letter  that  has  no  special  meaning causes an error, thus reserving
+        these combinations for future expansion. By  default,  as  in  Perl,  a
+        backslash  followed by a letter with no special meaning is treated as a
+        literal. (Perl can, however, be persuaded to give a warning for  this.)
+        There  are  at  present no other features controlled by this option. It
+        can also be set by a (?X) option setting within a pattern.
+          PCRE_FIRSTLINE
+        If this option is set, an  unanchored  pattern  is  required  to  match
+        before  or  at  the  first  newline  in  the subject string, though the
+        matched text may continue over the newline.
+          PCRE_MULTILINE
+        By default, PCRE treats the subject string as consisting  of  a  single
+        line  of characters (even if it actually contains newlines). The "start
+        of line" metacharacter (^) matches only at the  start  of  the  string,
+        while  the  "end  of line" metacharacter ($) matches only at the end of
+        the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
+        is set). This is the same as Perl.
+        When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"
+        constructs match immediately following or immediately  before  internal
+        newlines  in  the  subject string, respectively, as well as at the very
+        start and end. This is equivalent to Perl's /m option, and  it  can  be
+        changed within a pattern by a (?m) option setting. If there are no new-
+        lines in a subject string, or no occurrences of ^ or $  in  a  pattern,
+        setting PCRE_MULTILINE has no effect.
+          PCRE_NEWLINE_CR
+          PCRE_NEWLINE_LF
+          PCRE_NEWLINE_CRLF
+          PCRE_NEWLINE_ANYCRLF
+          PCRE_NEWLINE_ANY
+        These  options  override the default newline definition that was chosen
+        when PCRE was built. Setting the first or the second specifies  that  a
+        newline  is  indicated  by a single character (CR or LF, respectively).
+        Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
+        two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
+        that any of the three preceding sequences should be recognized. Setting
+        PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
+        recognized. The Unicode newline sequences are the three just mentioned,
+        plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
+        U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
+        (paragraph  separator,  U+2029).  The  last  two are recognized only in
+        UTF-8 mode.
+        The newline setting in the  options  word  uses  three  bits  that  are
+        treated as a number, giving eight possibilities. Currently only six are
+        used (default plus the five values above). This means that if  you  set
+        more  than one newline option, the combination may or may not be sensi-
+        ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
+        PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
+        cause an error.
+        The only time that a line break is specially recognized when  compiling
+        a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
+        character class is encountered. This indicates  a  comment  that  lasts
+        until  after the next line break sequence. In other circumstances, line
+        break  sequences  are  treated  as  literal  data,   except   that   in
+        PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
+        and are therefore ignored.
+        The newline option that is set at compile time becomes the default that
+        is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
+          PCRE_NO_AUTO_CAPTURE
+        If this option is set, it disables the use of numbered capturing paren-
+        theses  in the pattern. Any opening parenthesis that is not followed by
+        ? behaves as if it were followed by ?: but named parentheses can  still
+        be  used  for  capturing  (and  they acquire numbers in the usual way).
+        There is no equivalent of this option in Perl.
+          PCRE_UNGREEDY
+        This option inverts the "greediness" of the quantifiers  so  that  they
+        are  not greedy by default, but become greedy if followed by "?". It is
+        not compatible with Perl. It can also be set by a (?U)  option  setting
+        within the pattern.
+          PCRE_UTF8
+        This  option  causes PCRE to regard both the pattern and the subject as
+        strings of UTF-8 characters instead of single-byte  character  strings.
+        However,  it is available only when PCRE is built to include UTF-8 sup-
+        port. If not, the use of this option provokes an error. Details of  how
+        this  option  changes the behaviour of PCRE are given in the section on
+        UTF-8 support in the main pcre page.
+          PCRE_NO_UTF8_CHECK
+        When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
+        automatically  checked. If an invalid UTF-8 sequence of bytes is found,
+        pcre_compile() returns an error. If you already know that your  pattern
+        is  valid, and you want to skip this check for performance reasons, you
+        can set the PCRE_NO_UTF8_CHECK option. When it is set,  the  effect  of
+        passing an invalid UTF-8 string as a pattern is undefined. It may cause
+        your program to crash.  Note that this option can  also  be  passed  to
+        pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-
+        ing of subject strings.
+ COMPILATION ERROR CODES
+        The following table lists the error  codes  than  may  be  returned  by
+        pcre_compile2(),  along with the error messages that may be returned by
+        both compiling functions. As PCRE has developed, some error codes  have
+        fallen out of use. To avoid confusion, they have not been re-used.
+ no error
+ \ at end of pattern
+ \c at end of pattern
+ unrecognized character follows \
+ numbers out of order in {} quantifier
+ number too big in {} quantifier
+ missing terminating ] for character class
+ invalid escape sequence in character class
+ range out of order in character class
+ nothing to repeat
+ [this code is not in use]
+ internal error: unexpected repeat
+ unrecognized character after (?
+ POSIX named classes are supported only within a class
+ missing )
+ reference to non-existent subpattern
+ erroffset passed as NULL
+ unknown option bit(s) set
+ missing ) after comment
+ [this code is not in use]
+ regular expression too large
+ failed to get memory
+ unmatched parentheses
+ internal error: code overflow
+ unrecognized character after (?<
+ lookbehind assertion is not fixed length
+ malformed number or name after (?(
+ conditional group contains more than two branches
+ assertion expected after (?(
+ (?R or (?digits must be followed by )
+ unknown POSIX class name
+ POSIX collating elements are not supported
+ this version of PCRE is not compiled with PCRE_UTF8 support
+ [this code is not in use]
+ character value in \x{...} sequence is too large
+ invalid condition (?(0)
+ \C not allowed in lookbehind assertion
+ PCRE does not support \L, \l, \N, \U, or \u
+ number after (?C is > 255
+ closing ) for (?C expected
+ recursive call could loop indefinitely
+ unrecognized character after (?P
+ syntax error in subpattern name (missing terminator)
+ two named subpatterns have the same name
+ invalid UTF-8 string
+ support for \P, \p, and \X has not been compiled
+ malformed \P or \p sequence
+ unknown property name after \P or \p
+ subpattern name is too long (maximum 32 characters)
+ too many named subpatterns (maximum 10,000)
+ repeated subpattern is too long
+ octal value is greater than \377 (not in UTF-8 mode)
+ internal error: overran compiling workspace
+  internal  error:  previously-checked  referenced  subpattern not
+        found
+ DEFINE group contains more than one branch
+ repeating a DEFINE group is not allowed
+ inconsistent NEWLINE options"
  STUDYING A PATTERN
-      When a pattern is going to be  used  several  times,  it  is
-      worth  spending  more time analyzing it in order to speed up
-      the time taken for matching. The function pcre_study() takes
-      a  pointer  to a compiled pattern as its first argument, and
-      returns a  pointer  to  a  pcre_extra  block  (another  void
-      typedef)  containing  additional  information about the pat-
-      tern; this can be passed to pcre_exec().  If  no  additional
-      information is available, NULL is returned.
-      The second argument contains option  bits.  At  present,  no
-      options  are  defined  for  pcre_study(),  and this argument
-      should always be zero.
-      The third argument for pcre_study() is a pointer to an error
-      message. If studying succeeds (even if no data is returned),
-      the variable it points to  is  set  to  NULL.  Otherwise  it
-      points to a textual error message.
-      At present, studying a  pattern  is  useful  only  for  non-
-      anchored  patterns  that do not have a single fixed starting
-      character. A  bitmap  of  possible  starting  characters  is
-      created.
+        pcre_extra *pcre_study(const pcre *code, int options
+             const char **errptr);
+        If a compiled pattern is going to be used several times,  it  is  worth
+        spending more time analyzing it in order to speed up the time taken for
+        matching. The function pcre_study() takes a pointer to a compiled  pat-
+        tern as its first argument. If studying the pattern produces additional
+        information that will help speed up matching,  pcre_study()  returns  a
+        pointer  to a pcre_extra block, in which the study_data field points to
+        the results of the study.
+        The  returned  value  from  pcre_study()  can  be  passed  directly  to
+        pcre_exec().  However,  a  pcre_extra  block also contains other fields
+        that can be set by the caller before the block  is  passed;  these  are
+        described below in the section on matching a pattern.
+        If  studying  the  pattern  does not produce any additional information
+        pcre_study() returns NULL. In that circumstance, if the calling program
+        wants  to  pass  any of the other fields to pcre_exec(), it must set up
+        its own pcre_extra block.
+        The second argument of pcre_study() contains option bits.  At  present,
+        no options are defined, and this argument should always be zero.
+        The  third argument for pcre_study() is a pointer for an error message.
+        If studying succeeds (even if no data is  returned),  the  variable  it
+        points  to  is  set  to NULL. Otherwise it is set to point to a textual
+        error message. This is a static string that is part of the library. You
+        must  not  try  to  free it. You should test the error pointer for NULL
+        after calling pcre_study(), to be sure that it has run successfully.
+        This is a typical call to pcre_study():
+          pcre_extra *pe;
+          pe = pcre_study(
+            re,             /* result of pcre_compile() */
+,              /* no options exist */
+            &error);        /* set to NULL or points to a message */
+        At present, studying a pattern is useful only for non-anchored patterns
+        that  do not have a single fixed starting character. A bitmap of possi-
+        ble starting bytes is created.
  LOCALE SUPPORT
-      PCRE handles caseless matching, and determines whether char-
-      acters  are  letters, digits, or whatever, by reference to a
-      set of tables. The library contains a default set of  tables
-      which  is  created in the default C locale when PCRE is com-
-      piled.  This  is   used   when   the   final   argument   of
-      pcre_compile()  is NULL, and is sufficient for many applica-
-      tions.
-      An alternative set of tables can, however, be supplied. Such
-      tables  are built by calling the pcre_maketables() function,
-      which has no arguments, in the relevant locale.  The  result
-      can  then be passed to pcre_compile() as often as necessary.
-      For example, to build and use tables  that  are  appropriate
-      for  the French locale (where accented characters with codes
-      greater than 128 are treated as letters), the following code
-      could be used:
-        setlocale(LC_CTYPE, "fr");
-        tables = pcre_maketables();
-        re = pcre_compile(..., tables);
-      The  tables  are  built  in  memory  that  is  obtained  via
-      pcre_malloc.  The  pointer that is passed to pcre_compile is
-      saved with the compiled pattern, and  the  same  tables  are
-      used  via this pointer by pcre_study() and pcre_exec(). Thus
-      for any single pattern, compilation, studying  and  matching
-      all happen in the same locale, but different patterns can be
-      compiled in different locales. It is the caller's  responsi-
-      bility  to  ensure  that  the  memory  containing the tables
-      remains available for as long as it is needed.
+        PCRE handles caseless matching, and determines whether  characters  are
+        letters,  digits, or whatever, by reference to a set of tables, indexed
+        by character value. When running in UTF-8 mode, this  applies  only  to
+        characters  with  codes  less than 128. Higher-valued codes never match
+        escapes such as \w or \d, but can be tested with \p if  PCRE  is  built
+        with  Unicode  character property support. The use of locales with Uni-
+        code is discouraged. If you are handling characters with codes  greater
+        than  128, you should either use UTF-8 and Unicode, or use locales, but
+        not try to mix the two.
+        PCRE contains an internal set of tables that are used  when  the  final
+        argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
+        applications.  Normally, the internal tables recognize only ASCII char-
+        acters. However, when PCRE is built, it is possible to cause the inter-
+        nal tables to be rebuilt in the default "C" locale of the local system,
+        which may cause them to be different.
+        The  internal tables can always be overridden by tables supplied by the
+        application that calls PCRE. These may be created in a different locale
+        from  the  default.  As more and more applications change to using Uni-
+        code, the need for this locale support is expected to die away.
+        External tables are built by calling  the  pcre_maketables()  function,
+        which  has no arguments, in the relevant locale. The result can then be
+        passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
+        example,  to  build  and use tables that are appropriate for the French
+        locale (where accented characters with  values  greater  than  128  are
+        treated as letters), the following code could be used:
+          setlocale(LC_CTYPE, "fr_FR");
+          tables = pcre_maketables();
+          re = pcre_compile(..., tables);
+        The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
+        if you are using Windows, the name for the French locale is "french".
+        When pcre_maketables() runs, the tables are built  in  memory  that  is
+        obtained  via  pcre_malloc. It is the caller's responsibility to ensure
+        that the memory containing the tables remains available for as long  as
+        it is needed.
+        The pointer that is passed to pcre_compile() is saved with the compiled
+        pattern, and the same tables are used via this pointer by  pcre_study()
+        and normally also by pcre_exec(). Thus, by default, for any single pat-
+        tern, compilation, studying and matching all happen in the same locale,
+        but different patterns can be compiled in different locales.
+        It  is  possible to pass a table pointer or NULL (indicating the use of
+        the internal tables) to pcre_exec(). Although  not  intended  for  this
+        purpose,  this facility could be used to match a pattern in a different
+        locale from the one in which it was compiled. Passing table pointers at
+        run time is discussed below in the section on matching a pattern.
  INFORMATION ABOUT A PATTERN
-      The pcre_info() function returns information  about  a  com-
-      piled pattern.  Its yield is the number of capturing subpat-
-      terns, or one of the following negative numbers:
-        PCRE_ERROR_NULL       the argument code was NULL
-        PCRE_ERROR_BADMAGIC   the "magic number" was not found
-      If the optptr argument is not NULL, a copy  of  the  options
-      with which the pattern was compiled is placed in the integer
-      it points to. These option bits are those specified  in  the
-      call  to  pcre_compile(),  modified  by any top-level option
-      settings  within  the   pattern   itself,   and   with   the
-      PCRE_ANCHORED  bit  set  if  the form of the pattern implies
-      that it can match only at the start of a subject string.
-      If the pattern is not anchored and the firstcharptr argument
-      is  not  NULL, it is used to pass back information about the
-      first character of any matched string. If there is  a  fixed
-      first    character,    e.g.   from   a   pattern   such   as
-      (cat|cow|coyote), then it is returned in the integer pointed
-      to by firstcharptr. Otherwise, if either
-      (a) the pattern was compiled with the PCRE_MULTILINE option,
-      and every branch starts with "^", or
-      (b) every  branch  of  the  pattern  starts  with  ".*"  and
-      PCRE_DOTALL is not set (if it were set, the pattern would be
-      anchored),
-      then -1 is returned, indicating  that  the  pattern  matches
-      only  at  the  start  of  a subject string or after any "\n"
-      within the string. Otherwise -2 is returned.
+        int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
+             int what, void *where);
+        The  pcre_fullinfo() function returns information about a compiled pat-
+        tern. It replaces the obsolete pcre_info() function, which is neverthe-
+        less retained for backwards compability (and is documented below).
+        The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
+        pattern. The second argument is the result of pcre_study(), or NULL  if
+        the  pattern  was not studied. The third argument specifies which piece
+        of information is required, and the fourth argument is a pointer  to  a
+        variable  to  receive  the  data. The yield of the function is zero for
+        success, or one of the following negative numbers:
+          PCRE_ERROR_NULL       the argument code was NULL
+                                the argument where was NULL
+          PCRE_ERROR_BADMAGIC   the "magic number" was not found
+          PCRE_ERROR_BADOPTION  the value of what was invalid
+        The "magic number" is placed at the start of each compiled  pattern  as
+        an  simple check against passing an arbitrary memory pointer. Here is a
+        typical call of pcre_fullinfo(), to obtain the length of  the  compiled
+        pattern:
+          int rc;
+          size_t length;
+          rc = pcre_fullinfo(
+            re,               /* result of pcre_compile() */
+            pe,               /* result of pcre_study(), or NULL */
+            PCRE_INFO_SIZE,   /* what is required */
+            &length);         /* where to put the data */
+        The  possible  values for the third argument are defined in pcre.h, and
+        are as follows:
+          PCRE_INFO_BACKREFMAX
+        Return the number of the highest back reference  in  the  pattern.  The
+        fourth  argument  should  point to an int variable. Zero is returned if
+        there are no back references.
+          PCRE_INFO_CAPTURECOUNT
+        Return the number of capturing subpatterns in the pattern.  The  fourth
+        argument should point to an int variable.
+          PCRE_INFO_DEFAULT_TABLES
+        Return  a pointer to the internal default character tables within PCRE.
+        The fourth argument should point to an unsigned char *  variable.  This
+        information call is provided for internal use by the pcre_study() func-
+        tion. External callers can cause PCRE to use  its  internal  tables  by
+        passing a NULL table pointer.
+          PCRE_INFO_FIRSTBYTE
+        Return  information  about  the first byte of any matched string, for a
+        non-anchored pattern. The fourth argument should point to an int  vari-
+        able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
+        is still recognized for backwards compatibility.)
+        If there is a fixed first byte, for example, from  a  pattern  such  as
+        (cat|cow|coyote), its value is returned. Otherwise, if either
+        (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
+        branch starts with "^", or
+        (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
+        set (if it were set, the pattern would be anchored),
+        -1  is  returned, indicating that the pattern matches only at the start
+        of a subject string or after any newline within the  string.  Otherwise
+        -2 is returned. For anchored patterns, -2 is returned.
+          PCRE_INFO_FIRSTTABLE
+        If  the pattern was studied, and this resulted in the construction of a
+-bit table indicating a fixed set of bytes for the first byte in any
+        matching  string, a pointer to the table is returned. Otherwise NULL is
+        returned. The fourth argument should point to an unsigned char *  vari-
+        able.
+          PCRE_INFO_LASTLITERAL
+        Return  the  value of the rightmost literal byte that must exist in any
+        matched string, other than at its  start,  if  such  a  byte  has  been
+        recorded. The fourth argument should point to an int variable. If there
+        is no such byte, -1 is returned. For anchored patterns, a last  literal
+        byte  is  recorded only if it follows something of variable length. For
+        example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
+        /^a\dz\d/ the returned value is -1.
+          PCRE_INFO_NAMECOUNT
+          PCRE_INFO_NAMEENTRYSIZE
+          PCRE_INFO_NAMETABLE
+        PCRE  supports the use of named as well as numbered capturing parenthe-
+        ses. The names are just an additional way of identifying the  parenthe-
+        ses, which still acquire numbers. Several convenience functions such as
+        pcre_get_named_substring() are provided for  extracting  captured  sub-
+        strings  by  name. It is also possible to extract the data directly, by
+        first converting the name to a number in order to  access  the  correct
+        pointers in the output vector (described with pcre_exec() below). To do
+        the conversion, you need  to  use  the  name-to-number  map,  which  is
+        described by these three values.
+        The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
+        gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
+        of  each  entry;  both  of  these  return  an int value. The entry size
+        depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
+        a  pointer  to  the  first  entry of the table (a pointer to char). The
+        first two bytes of each entry are the number of the capturing parenthe-
+        sis,  most  significant byte first. The rest of the entry is the corre-
+        sponding name, zero terminated. The names are  in  alphabetical  order.
+        When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
+        theses numbers. For example, consider  the  following  pattern  (assume
+        PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
+        ignored):
+          (?<date> (?<year>(\d\d)?\d\d) -
+          (?<month>\d\d) - (?<day>\d\d) )
+        There are four named subpatterns, so the table has  four  entries,  and
+        each  entry  in the table is eight bytes long. The table is as follows,
+        with non-printing bytes shows in hexadecimal, and undefined bytes shown
+        as ??:
+01 d  a  t  e  00 ??
+05 d  a  y  00 ?? ??
+04 m  o  n  t  h  00
+02 y  e  a  r  00 ??
+        When  writing  code  to  extract  data from named subpatterns using the
+        name-to-number map, remember that the length of the entries  is  likely
+        to be different for each compiled pattern.
+          PCRE_INFO_OPTIONS
+        Return  a  copy of the options with which the pattern was compiled. The
+        fourth argument should point to an unsigned long  int  variable.  These
+        option bits are those specified in the call to pcre_compile(), modified
+        by any top-level option settings within the pattern itself.
+        A pattern is automatically anchored by PCRE if  all  of  its  top-level
+        alternatives begin with one of the following:
+          ^     unless PCRE_MULTILINE is set
+          \A    always
+          \G    always
+          .*    if PCRE_DOTALL is set and there are no back
+                  references to the subpattern in which .* appears
+        For such patterns, the PCRE_ANCHORED bit is set in the options returned
+        by pcre_fullinfo().
+          PCRE_INFO_SIZE
+        Return the size of the compiled pattern, that is, the  value  that  was
+        passed as the argument to pcre_malloc() when PCRE was getting memory in
+        which to place the compiled data. The fourth argument should point to a
+        size_t variable.
+          PCRE_INFO_STUDYSIZE
+        Return the size of the data block pointed to by the study_data field in
+        a pcre_extra block. That is,  it  is  the  value  that  was  passed  to
+        pcre_malloc() when PCRE was getting memory into which to place the data
+        created by pcre_study(). The fourth argument should point to  a  size_t
+        variable.
+ OBSOLETE INFO FUNCTION
+        int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
+        The  pcre_info()  function is now obsolete because its interface is too
+        restrictive to return all the available data about a compiled  pattern.
+        New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
+        pcre_info() is the number of capturing subpatterns, or one of the  fol-
+        lowing negative numbers:
+          PCRE_ERROR_NULL       the argument code was NULL
+          PCRE_ERROR_BADMAGIC   the "magic number" was not found
+        If  the  optptr  argument is not NULL, a copy of the options with which
+        the pattern was compiled is placed in the integer  it  points  to  (see
+        PCRE_INFO_OPTIONS above).
+        If  the  pattern  is  not anchored and the firstcharptr argument is not
+        NULL, it is used to pass back information about the first character  of
+        any matched string (see PCRE_INFO_FIRSTBYTE above).
+ REFERENCE COUNTS
+        int pcre_refcount(pcre *code, int adjust);
+        The  pcre_refcount()  function is used to maintain a reference count in
+        the data block that contains a compiled pattern. It is provided for the
+        benefit  of  applications  that  operate  in an object-oriented manner,
+        where different parts of the application may be using the same compiled
+        pattern, but you want to free the block when they are all done.
+        When a pattern is compiled, the reference count field is initialized to
+        zero.  It is changed only by calling this function, whose action is  to
+        add  the  adjust  value  (which may be positive or negative) to it. The
+        yield of the function is the new value. However, the value of the count
+        is  constrained to lie between 0 and 65535, inclusive. If the new value
+        is outside these limits, it is forced to the appropriate limit value.
+        Except when it is zero, the reference count is not correctly  preserved
+        if  a  pattern  is  compiled on one host and then transferred to a host
+        whose byte-order is different. (This seems a highly unlikely scenario.)
+ MATCHING A PATTERN: THE TRADITIONAL FUNCTION
+        int pcre_exec(const pcre *code, const pcre_extra *extra,
+             const char *subject, int length, int startoffset,
+             int options, int *ovector, int ovecsize);
+        The  function pcre_exec() is called to match a subject string against a
+        compiled pattern, which is passed in the code argument. If the  pattern
+        has been studied, the result of the study should be passed in the extra
+        argument. This function is the main matching facility of  the  library,
+        and it operates in a Perl-like manner. For specialist use there is also
+        an alternative matching function, which is described below in the  sec-
+        tion about the pcre_dfa_exec() function.
+        In  most applications, the pattern will have been compiled (and option-
+        ally studied) in the same process that calls pcre_exec().  However,  it
+        is possible to save compiled patterns and study data, and then use them
+        later in different processes, possibly even on different hosts.  For  a
+        discussion about this, see the pcreprecompile documentation.
+        Here is an example of a simple call to pcre_exec():
+          int rc;
+          int ovector[30];
+          rc = pcre_exec(
+            re,             /* result of pcre_compile() */
+            NULL,           /* we didn't study the pattern */
+            "some string",  /* the subject string */
+,             /* the length of the subject string */
+,              /* start at offset 0 in the subject */
+,              /* default options */
+            ovector,        /* vector of integers for substring information */
+);            /* number of elements (NOT size in bytes) */
+    Extra data for pcre_exec()
+        If  the  extra argument is not NULL, it must point to a pcre_extra data
+        block. The pcre_study() function returns such a block (when it  doesn't
+        return  NULL), but you can also create one for yourself, and pass addi-
+        tional information in it. The pcre_extra block contains  the  following
+        fields (not necessarily in this order):
+          unsigned long int flags;
+          void *study_data;
+          unsigned long int match_limit;
+          unsigned long int match_limit_recursion;
+          void *callout_data;
+          const unsigned char *tables;
+        The  flags  field  is a bitmap that specifies which of the other fields
+        are set. The flag bits are:
+          PCRE_EXTRA_STUDY_DATA
+          PCRE_EXTRA_MATCH_LIMIT
+          PCRE_EXTRA_MATCH_LIMIT_RECURSION
+          PCRE_EXTRA_CALLOUT_DATA
+          PCRE_EXTRA_TABLES
+        Other flag bits should be set to zero. The study_data field is  set  in
+        the  pcre_extra  block  that is returned by pcre_study(), together with
+        the appropriate flag bit. You should not set this yourself, but you may
+        add  to  the  block by setting the other fields and their corresponding
+        flag bits.
+        The match_limit field provides a means of preventing PCRE from using up
+        a  vast amount of resources when running patterns that are not going to
+        match, but which have a very large number  of  possibilities  in  their
+        search  trees.  The  classic  example  is  the  use of nested unlimited
+        repeats.
+        Internally, PCRE uses a function called match() which it calls  repeat-
+        edly  (sometimes  recursively). The limit set by match_limit is imposed
+        on the number of times this function is called during  a  match,  which
+        has  the  effect  of  limiting the amount of backtracking that can take
+        place. For patterns that are not anchored, the count restarts from zero
+        for each position in the subject string.
+        The  default  value  for  the  limit can be set when PCRE is built; the
+        default default is 10 million, which handles all but the  most  extreme
+        cases.  You  can  override  the  default by suppling pcre_exec() with a
+        pcre_extra    block    in    which    match_limit    is    set,     and
+        PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
+        exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
+        The match_limit_recursion field is similar to match_limit, but  instead
+        of limiting the total number of times that match() is called, it limits
+        the depth of recursion. The recursion depth is a  smaller  number  than
+        the  total number of calls, because not all calls to match() are recur-
+        sive.  This limit is of use only if it is set smaller than match_limit.
+        Limiting  the  recursion  depth  limits the amount of stack that can be
+        used, or, when PCRE has been compiled to use memory on the heap instead
+        of the stack, the amount of heap memory that can be used.
+        The  default  value  for  match_limit_recursion can be set when PCRE is
+        built; the default default  is  the  same  value  as  the  default  for
+        match_limit.  You can override the default by suppling pcre_exec() with
+        a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
+        PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
+        limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
+        The pcre_callout field is used in conjunction with the  "callout"  fea-
+        ture, which is described in the pcrecallout documentation.
+        The  tables  field  is  used  to  pass  a  character  tables pointer to
+        pcre_exec(); this overrides the value that is stored with the  compiled
+        pattern.  A  non-NULL value is stored with the compiled pattern only if
+        custom tables were supplied to pcre_compile() via  its  tableptr  argu-
+        ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
+        PCRE's internal tables to be used. This facility is  helpful  when  re-
+        using  patterns  that  have been saved after compiling with an external
+        set of tables, because the external tables  might  be  at  a  different
+        address  when  pcre_exec() is called. See the pcreprecompile documenta-
+        tion for a discussion of saving compiled patterns for later use.
+    Option bits for pcre_exec()
+        The unused bits of the options argument for pcre_exec() must  be  zero.
+        The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
+        PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
+        PCRE_PARTIAL.
+          PCRE_ANCHORED
+        The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
+        matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
+        turned  out to be anchored by virtue of its contents, it cannot be made
+        unachored at matching time.
+          PCRE_NEWLINE_CR
+          PCRE_NEWLINE_LF
+          PCRE_NEWLINE_CRLF
+          PCRE_NEWLINE_ANYCRLF
+          PCRE_NEWLINE_ANY
+        These options override  the  newline  definition  that  was  chosen  or
+        defaulted  when the pattern was compiled. For details, see the descrip-
+        tion of pcre_compile()  above.  During  matching,  the  newline  choice
+        affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
+        ters. It may also alter the way the match position is advanced after  a
+        match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,
+        PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is set, and a  match  attempt
+        fails  when the current position is at a CRLF sequence, the match posi-
+        tion is advanced by two characters instead of one, in other  words,  to
+        after the CRLF.
+          PCRE_NOTBOL
+        This option specifies that first character of the subject string is not
+        the beginning of a line, so the  circumflex  metacharacter  should  not
+        match  before it. Setting this without PCRE_MULTILINE (at compile time)
+        causes circumflex never to match. This option affects only  the  behav-
+        iour of the circumflex metacharacter. It does not affect \A.
+          PCRE_NOTEOL
+        This option specifies that the end of the subject string is not the end
+        of a line, so the dollar metacharacter should not match it nor  (except
+        in  multiline mode) a newline immediately before it. Setting this with-
+        out PCRE_MULTILINE (at compile time) causes dollar never to match. This
+        option  affects only the behaviour of the dollar metacharacter. It does
+        not affect \Z or \z.
+          PCRE_NOTEMPTY
+        An empty string is not considered to be a valid match if this option is
+        set.  If  there are alternatives in the pattern, they are tried. If all
+        the alternatives match the empty string, the entire  match  fails.  For
+        example, if the pattern
+          a?b?
+        is  applied  to  a string not beginning with "a" or "b", it matches the
+        empty string at the start of the subject. With PCRE_NOTEMPTY set,  this
+        match is not valid, so PCRE searches further into the string for occur-
+        rences of "a" or "b".
+        Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
+        cial  case  of  a  pattern match of the empty string within its split()
+        function, and when using the /g modifier. It  is  possible  to  emulate
+        Perl's behaviour after matching a null string by first trying the match
+        again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
+        if  that  fails by advancing the starting offset (see below) and trying
+        an ordinary match again. There is some code that demonstrates how to do
+        this in the pcredemo.c sample program.
+          PCRE_NO_UTF8_CHECK
+        When PCRE_UTF8 is set at compile time, the validity of the subject as a
+        UTF-8 string is automatically checked when pcre_exec() is  subsequently
+        called.   The  value  of  startoffset is also checked to ensure that it
+        points to the start of a UTF-8 character. If an invalid UTF-8  sequence
+        of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If
+        startoffset contains an  invalid  value,  PCRE_ERROR_BADUTF8_OFFSET  is
+        returned.
+        If  you  already  know that your subject is valid, and you want to skip
+        these   checks   for   performance   reasons,   you   can    set    the
+        PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
+        do this for the second and subsequent calls to pcre_exec() if  you  are
+        making  repeated  calls  to  find  all  the matches in a single subject
+        string. However, you should be  sure  that  the  value  of  startoffset
+        points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
+        set, the effect of passing an invalid UTF-8 string as a subject,  or  a
+        value  of startoffset that does not point to the start of a UTF-8 char-
+        acter, is undefined. Your program may crash.
+          PCRE_PARTIAL
+        This option turns on the  partial  matching  feature.  If  the  subject
+        string  fails to match the pattern, but at some point during the match-
+        ing process the end of the subject was reached (that  is,  the  subject
+        partially  matches  the  pattern and the failure to match occurred only
+        because there were not enough subject characters), pcre_exec()  returns
+        PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
+        used, there are restrictions on what may appear in the  pattern.  These
+        are discussed in the pcrepartial documentation.
+    The string to be matched by pcre_exec()
+        The  subject string is passed to pcre_exec() as a pointer in subject, a
+        length in length, and a starting byte offset in startoffset.  In  UTF-8
+        mode,  the  byte  offset  must point to the start of a UTF-8 character.
+        Unlike the pattern string, the subject may contain binary  zero  bytes.
+        When  the starting offset is zero, the search for a match starts at the
+        beginning of the subject, and this is by far the most common case.
+        A non-zero starting offset is useful when searching for  another  match
+        in  the same subject by calling pcre_exec() again after a previous suc-
+        cess.  Setting startoffset differs from just passing over  a  shortened
+        string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
+        with any kind of lookbehind. For example, consider the pattern
+          \Biss\B
+        which finds occurrences of "iss" in the middle of  words.  (\B  matches
+        only  if  the  current position in the subject is not a word boundary.)
+        When applied to the string "Mississipi" the first call  to  pcre_exec()
+        finds  the  first  occurrence. If pcre_exec() is called again with just
+        the remainder of the subject,  namely  "issipi",  it  does  not  match,
+        because \B is always false at the start of the subject, which is deemed
+        to be a word boundary. However, if pcre_exec()  is  passed  the  entire
+        string again, but with startoffset set to 4, it finds the second occur-
+        rence of "iss" because it is able to look behind the starting point  to
+        discover that it is preceded by a letter.
+        If  a  non-zero starting offset is passed when the pattern is anchored,
+        one attempt to match at the given offset is made. This can only succeed
+        if  the  pattern  does  not require the match to be at the start of the
+        subject.
+    How pcre_exec() returns captured substrings
+        In general, a pattern matches a certain portion of the subject, and  in
+        addition,  further  substrings  from  the  subject may be picked out by
+        parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
+        this  is  called "capturing" in what follows, and the phrase "capturing
+        subpattern" is used for a fragment of a pattern that picks out  a  sub-
+        string.  PCRE  supports several other kinds of parenthesized subpattern
+        that do not cause substrings to be captured.
+        Captured substrings are returned to the caller via a vector of  integer
+        offsets  whose  address is passed in ovector. The number of elements in
+        the vector is passed in ovecsize, which must be a non-negative  number.
+        Note: this argument is NOT the size of ovector in bytes.
+        The  first  two-thirds of the vector is used to pass back captured sub-
+        strings, each substring using a pair of integers. The  remaining  third
+        of  the  vector is used as workspace by pcre_exec() while matching cap-
+        turing subpatterns, and is not available for passing back  information.
+        The  length passed in ovecsize should always be a multiple of three. If
+        it is not, it is rounded down.
+        When a match is successful, information about  captured  substrings  is
+        returned  in  pairs  of integers, starting at the beginning of ovector,
+        and continuing up to two-thirds of its length at the  most.  The  first
+        element of a pair is set to the offset of the first character in a sub-
+        string, and the second is set to the  offset  of  the  first  character
+        after  the  end  of  a  substring. The first pair, ovector[0] and ovec-
+        tor[1], identify the portion of  the  subject  string  matched  by  the
+        entire  pattern.  The next pair is used for the first capturing subpat-
+        tern, and so on. The value returned by pcre_exec() is one more than the
+        highest numbered pair that has been set. For example, if two substrings
+        have been captured, the returned value is 3. If there are no  capturing
+        subpatterns,  the return value from a successful match is 1, indicating
+        that just the first pair of offsets has been set.
+        If a capturing subpattern is matched repeatedly, it is the last portion
+        of the string that it matched that is returned.
+        If  the vector is too small to hold all the captured substring offsets,
+        it is used as far as possible (up to two-thirds of its length), and the
+        function  returns a value of zero. In particular, if the substring off-
+        sets are not of interest, pcre_exec() may be called with ovector passed
+        as  NULL  and  ovecsize  as zero. However, if the pattern contains back
+        references and the ovector is not big enough to  remember  the  related
+        substrings,  PCRE has to get additional memory for use during matching.
+        Thus it is usually advisable to supply an ovector.
+        The pcre_info() function can be used to find  out  how  many  capturing
+        subpatterns  there  are  in  a  compiled pattern. The smallest size for
+        ovector that will allow for n captured substrings, in addition  to  the
+        offsets of the substring matched by the whole pattern, is (n+1)*3.
+        It  is  possible for capturing subpattern number n+1 to match some part
+        of the subject when subpattern n has not been used at all. For example,
+        if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the
+        return from the function is 4, and subpatterns 1 and 3 are matched, but
+ is  not.  When  this happens, both values in the offset pairs corre-
+        sponding to unused subpatterns are set to -1.
+        Offset values that correspond to unused subpatterns at the end  of  the
+        expression  are  also  set  to  -1. For example, if the string "abc" is
+        matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not
+        matched.  The  return  from the function is 2, because the highest used
+        capturing subpattern number is 1. However, you can refer to the offsets
+        for  the  second  and third capturing subpatterns if you wish (assuming
+        the vector is large enough, of course).
+        Some convenience functions are provided  for  extracting  the  captured
+        substrings as separate strings. These are described below.
+    Error return values from pcre_exec()
+        If  pcre_exec()  fails, it returns a negative number. The following are
+        defined in the header file:
+          PCRE_ERROR_NOMATCH        (-1)
+        The subject string did not match the pattern.
+          PCRE_ERROR_NULL           (-2)
+        Either code or subject was passed as NULL,  or  ovector  was  NULL  and
+        ovecsize was not zero.
+          PCRE_ERROR_BADOPTION      (-3)
+        An unrecognized bit was set in the options argument.
+          PCRE_ERROR_BADMAGIC       (-4)
+        PCRE  stores a 4-byte "magic number" at the start of the compiled code,
+        to catch the case when it is passed a junk pointer and to detect when a
+        pattern that was compiled in an environment of one endianness is run in
+        an environment with the other endianness. This is the error  that  PCRE
+        gives when the magic number is not present.
+          PCRE_ERROR_UNKNOWN_OPCODE (-5)
+        While running the pattern match, an unknown item was encountered in the
+        compiled pattern. This error could be caused by a bug  in  PCRE  or  by
+        overwriting of the compiled pattern.
+          PCRE_ERROR_NOMEMORY       (-6)
+        If  a  pattern contains back references, but the ovector that is passed
+        to pcre_exec() is not big enough to remember the referenced substrings,
+        PCRE  gets  a  block of memory at the start of matching to use for this
+        purpose. If the call via pcre_malloc() fails, this error is given.  The
+        memory is automatically freed at the end of matching.
+          PCRE_ERROR_NOSUBSTRING    (-7)
+        This  error is used by the pcre_copy_substring(), pcre_get_substring(),
+        and  pcre_get_substring_list()  functions  (see  below).  It  is  never
+        returned by pcre_exec().
+          PCRE_ERROR_MATCHLIMIT     (-8)
+        The  backtracking  limit,  as  specified  by the match_limit field in a
+        pcre_extra structure (or defaulted) was reached.  See  the  description
+        above.
+          PCRE_ERROR_CALLOUT        (-9)
+        This error is never generated by pcre_exec() itself. It is provided for
+        use by callout functions that want to yield a distinctive  error  code.
+        See the pcrecallout documentation for details.
+          PCRE_ERROR_BADUTF8        (-10)
+        A  string  that contains an invalid UTF-8 byte sequence was passed as a
+        subject.
+          PCRE_ERROR_BADUTF8_OFFSET (-11)
+        The UTF-8 byte sequence that was passed as a subject was valid, but the
+        value  of startoffset did not point to the beginning of a UTF-8 charac-
+        ter.
+          PCRE_ERROR_PARTIAL        (-12)
+        The subject string did not match, but it did match partially.  See  the
+        pcrepartial documentation for details of partial matching.
+          PCRE_ERROR_BADPARTIAL     (-13)
+        The  PCRE_PARTIAL  option  was  used with a compiled pattern containing
+        items that are not supported for partial matching. See the  pcrepartial
+        documentation for details of partial matching.
+          PCRE_ERROR_INTERNAL       (-14)
+        An  unexpected  internal error has occurred. This error could be caused
+        by a bug in PCRE or by overwriting of the compiled pattern.
+          PCRE_ERROR_BADCOUNT       (-15)
+        This error is given if the value of the ovecsize argument is  negative.
+          PCRE_ERROR_RECURSIONLIMIT (-21)
+        The internal recursion limit, as specified by the match_limit_recursion
+        field in a pcre_extra structure (or defaulted)  was  reached.  See  the
+        description above.
+          PCRE_ERROR_NULLWSLIMIT    (-22)
+        When  a  group  that  can  match an empty substring is repeated with an
+        unbounded upper limit, the subject position at the start of  the  group
+        must be remembered, so that a test for an empty string can be made when
+        the end of the group is reached. Some workspace is required  for  this;
+        if it runs out, this error is given.
+          PCRE_ERROR_BADNEWLINE     (-23)
+        An invalid combination of PCRE_NEWLINE_xxx options was given.
+        Error numbers -16 to -20 are not used by pcre_exec().
+ EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
+        int pcre_copy_substring(const char *subject, int *ovector,
+             int stringcount, int stringnumber, char *buffer,
+             int buffersize);
+        int pcre_get_substring(const char *subject, int *ovector,
+             int stringcount, int stringnumber,
+             const char **stringptr);
+        int pcre_get_substring_list(const char *subject,
+             int *ovector, int stringcount, const char ***listptr);
+        Captured  substrings  can  be  accessed  directly  by using the offsets
+        returned by pcre_exec() in  ovector.  For  convenience,  the  functions
+        pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
+        string_list() are provided for extracting captured substrings  as  new,
+        separate,  zero-terminated strings. These functions identify substrings
+        by number. The next section describes functions  for  extracting  named
+        substrings.
+        A  substring that contains a binary zero is correctly extracted and has
+        a further zero added on the end, but the result is not, of course, a  C
+        string.   However,  you  can  process such a string by referring to the
+        length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
+        string().  Unfortunately, the interface to pcre_get_substring_list() is
+        not adequate for handling strings containing binary zeros, because  the
+        end of the final string is not independently indicated.
+        The  first  three  arguments  are the same for all three of these func-
+        tions: subject is the subject string that has  just  been  successfully
+        matched, ovector is a pointer to the vector of integer offsets that was
+        passed to pcre_exec(), and stringcount is the number of substrings that
+        were  captured  by  the match, including the substring that matched the
+        entire regular expression. This is the value returned by pcre_exec() if
+        it  is greater than zero. If pcre_exec() returned zero, indicating that
+        it ran out of space in ovector, the value passed as stringcount  should
+        be the number of elements in the vector divided by three.
+        The  functions pcre_copy_substring() and pcre_get_substring() extract a
+        single substring, whose number is given as  stringnumber.  A  value  of
+        zero  extracts  the  substring that matched the entire pattern, whereas
+        higher values  extract  the  captured  substrings.  For  pcre_copy_sub-
+        string(),  the  string  is  placed  in buffer, whose length is given by
+        buffersize, while for pcre_get_substring() a new  block  of  memory  is
+        obtained  via  pcre_malloc,  and its address is returned via stringptr.
+        The yield of the function is the length of the  string,  not  including
+        the terminating zero, or one of these error codes:
+          PCRE_ERROR_NOMEMORY       (-6)
+        The  buffer  was too small for pcre_copy_substring(), or the attempt to
+        get memory failed for pcre_get_substring().
+          PCRE_ERROR_NOSUBSTRING    (-7)
+        There is no substring whose number is stringnumber.
+        The pcre_get_substring_list()  function  extracts  all  available  sub-
+        strings  and  builds  a list of pointers to them. All this is done in a
+        single block of memory that is obtained via pcre_malloc. The address of
+        the  memory  block  is returned via listptr, which is also the start of
+        the list of string pointers. The end of the list is marked  by  a  NULL
+        pointer.  The  yield  of  the function is zero if all went well, or the
+        error code
+          PCRE_ERROR_NOMEMORY       (-6)
+        if the attempt to get the memory block failed.
+        When any of these functions encounter a substring that is unset,  which
+        can  happen  when  capturing subpattern number n+1 matches some part of
+        the subject, but subpattern n has not been used at all, they return  an
+        empty string. This can be distinguished from a genuine zero-length sub-
+        string by inspecting the appropriate offset in ovector, which is  nega-
+        tive for unset substrings.
+        The  two convenience functions pcre_free_substring() and pcre_free_sub-
+        string_list() can be used to free the memory  returned  by  a  previous
+        call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
+        tively. They do nothing more than  call  the  function  pointed  to  by
+        pcre_free,  which  of course could be called directly from a C program.
+        However, PCRE is used in some situations where it is linked via a  spe-
+        cial   interface  to  another  programming  language  that  cannot  use
+        pcre_free directly; it is for these cases that the functions  are  pro-
+        vided.
+ EXTRACTING CAPTURED SUBSTRINGS BY NAME
+        int pcre_get_stringnumber(const pcre *code,
+             const char *name);
+        int pcre_copy_named_substring(const pcre *code,
+             const char *subject, int *ovector,
+             int stringcount, const char *stringname,
+             char *buffer, int buffersize);
+        int pcre_get_named_substring(const pcre *code,
+             const char *subject, int *ovector,
+             int stringcount, const char *stringname,
+             const char **stringptr);
+        To  extract a substring by name, you first have to find associated num-
+        ber.  For example, for this pattern
+          (a+)b(?<xxx>\d+)...
+        the number of the subpattern called "xxx" is 2. If the name is known to
+        be unique (PCRE_DUPNAMES was not set), you can find the number from the
+        name by calling pcre_get_stringnumber(). The first argument is the com-
+        piled pattern, and the second is the name. The yield of the function is
+        the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
+        subpattern of that name.
+        Given the number, you can extract the substring directly, or use one of
+        the functions described in the previous section. For convenience, there
+        are also two functions that do the whole job.
+        Most    of    the    arguments   of   pcre_copy_named_substring()   and
+        pcre_get_named_substring() are the same  as  those  for  the  similarly
+        named  functions  that extract by number. As these are described in the
+        previous section, they are not re-described here. There  are  just  two
+        differences:
+        First,  instead  of a substring number, a substring name is given. Sec-
+        ond, there is an extra argument, given at the start, which is a pointer
+        to  the compiled pattern. This is needed in order to gain access to the
+        name-to-number translation table.
+        These functions call pcre_get_stringnumber(), and if it succeeds,  they
+        then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
+        ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
+        behaviour may not be what you want (see the next section).
+ DUPLICATE SUBPATTERN NAMES
+        int pcre_get_stringtable_entries(const pcre *code,
+             const char *name, char **first, char **last);
+        When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
+        subpatterns are not required to  be  unique.  Normally,  patterns  with
+        duplicate  names  are such that in any one match, only one of the named
+        subpatterns participates. An example is shown in the pcrepattern  docu-
+        mentation. When duplicates are present, pcre_copy_named_substring() and
+        pcre_get_named_substring() return the first substring corresponding  to
+        the  given  name  that  is  set.  If  none  are set, an empty string is
+        returned.  The pcre_get_stringnumber() function returns one of the num-
+        bers  that are associated with the name, but it is not defined which it
+        is.
+        If you want to get full details of all captured substrings for a  given
+        name,  you  must  use  the pcre_get_stringtable_entries() function. The
+        first argument is the compiled pattern, and the second is the name. The
+        third  and  fourth  are  pointers to variables which are updated by the
+        function. After it has run, they point to the first and last entries in
+        the  name-to-number  table  for  the  given  name.  The function itself
+        returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
+        there  are none. The format of the table is described above in the sec-
+        tion entitled Information about a  pattern.   Given  all  the  relevant
+        entries  for the name, you can extract each of their numbers, and hence
+        the captured data, if any.
+ FINDING ALL POSSIBLE MATCHES
+        The traditional matching function uses a  similar  algorithm  to  Perl,
+        which stops when it finds the first match, starting at a given point in
+        the subject. If you want to find all possible matches, or  the  longest
+        possible  match,  consider using the alternative matching function (see
+        below) instead. If you cannot use the alternative function,  but  still
+        need  to  find all possible matches, you can kludge it up by making use
+        of the callout facility, which is described in the pcrecallout documen-
+        tation.
+        What you have to do is to insert a callout right at the end of the pat-
+        tern.  When your callout function is called, extract and save the  cur-
+        rent  matched  substring.  Then  return  1, which forces pcre_exec() to
+        backtrack and try other alternatives. Ultimately, when it runs  out  of
+        matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
+ MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
+        int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
+             const char *subject, int length, int startoffset,
+             int options, int *ovector, int ovecsize,
+             int *workspace, int wscount);
+        The  function  pcre_dfa_exec()  is  called  to  match  a subject string
+        against a compiled pattern, using a matching algorithm that  scans  the
+        subject  string  just  once, and does not backtrack. This has different
+        characteristics to the normal algorithm, and  is  not  compatible  with
+        Perl.  Some  of the features of PCRE patterns are not supported. Never-
+        theless, there are times when this kind of matching can be useful.  For
+        a discussion of the two matching algorithms, see the pcrematching docu-
+        mentation.
+        The arguments for the pcre_dfa_exec() function  are  the  same  as  for
+        pcre_exec(), plus two extras. The ovector argument is used in a differ-
+        ent way, and this is described below. The other  common  arguments  are
+        used  in  the  same way as for pcre_exec(), so their description is not
+        repeated here.
+        The two additional arguments provide workspace for  the  function.  The
+        workspace  vector  should  contain at least 20 elements. It is used for
+        keeping  track  of  multiple  paths  through  the  pattern  tree.  More
+        workspace  will  be  needed for patterns and subjects where there are a
+        lot of potential matches.
+        Here is an example of a simple call to pcre_dfa_exec():
+          int rc;
+          int ovector[10];
+          int wspace[20];
+          rc = pcre_dfa_exec(
+            re,             /* result of pcre_compile() */
+            NULL,           /* we didn't study the pattern */
+            "some string",  /* the subject string */
+,             /* the length of the subject string */
+,              /* start at offset 0 in the subject */
+,              /* default options */
+            ovector,        /* vector of integers for substring information */
+,             /* number of elements (NOT size in bytes) */
+            wspace,         /* working space vector */
+);            /* number of elements (NOT size in bytes) */
+    Option bits for pcre_dfa_exec()
+        The unused bits of the options argument  for  pcre_dfa_exec()  must  be
+        zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-
+        LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,
+        PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
+        three of these are the same as for pcre_exec(), so their description is
+        not repeated here.
+          PCRE_PARTIAL
+        This  has  the  same general effect as it does for pcre_exec(), but the
+        details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for
+        pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into
+        PCRE_ERROR_PARTIAL if the end of the subject  is  reached,  there  have
+        been no complete matches, but there is still at least one matching pos-
+        sibility. The portion of the string that provided the partial match  is
+        set as the first matching string.
+          PCRE_DFA_SHORTEST
+        Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
+        stop as soon as it has found one match. Because of the way the alterna-
+        tive  algorithm  works, this is necessarily the shortest possible match
+        at the first possible matching point in the subject string.
+          PCRE_DFA_RESTART
+        When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and
+        returns  a  partial  match, it is possible to call it again, with addi-
+        tional subject characters, and have it continue with  the  same  match.
+        The  PCRE_DFA_RESTART  option requests this action; when it is set, the
+        workspace and wscount options must reference the same vector as  before
+        because  data  about  the  match so far is left in them after a partial
+        match. There is more discussion of this  facility  in  the  pcrepartial
+        documentation.
+    Successful returns from pcre_dfa_exec()
+        When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
+        string in the subject. Note, however, that all the matches from one run
+        of  the  function  start  at the same point in the subject. The shorter
+        matches are all initial substrings of the longer matches. For  example,
+        if the pattern
+          <.*>
+        is matched against the string
+          This is <something> <something else> <something further> no more
+        the three matched strings are
+          <something>
+          <something> <something else>
+          <something> <something else> <something further>
+        On  success,  the  yield of the function is a number greater than zero,
+        which is the number of matched substrings.  The  substrings  themselves
+        are  returned  in  ovector. Each string uses two elements; the first is
+        the offset to the start, and the second is the offset to  the  end.  In
+        fact,  all  the  strings  have the same start offset. (Space could have
+        been saved by giving this only once, but it was decided to retain  some
+        compatibility  with  the  way pcre_exec() returns data, even though the
+        meaning of the strings is different.)
+        The strings are returned in reverse order of length; that is, the long-
+        est  matching  string is given first. If there were too many matches to
+        fit into ovector, the yield of the function is zero, and the vector  is
+        filled with the longest matches.
+    Error returns from pcre_dfa_exec()
+        The  pcre_dfa_exec()  function returns a negative number when it fails.
+        Many of the errors are the same  as  for  pcre_exec(),  and  these  are
+        described  above.   There are in addition the following errors that are
+        specific to pcre_dfa_exec():
+          PCRE_ERROR_DFA_UITEM      (-16)
+        This return is given if pcre_dfa_exec() encounters an item in the  pat-
+        tern  that  it  does not support, for instance, the use of \C or a back
+        reference.
+          PCRE_ERROR_DFA_UCOND      (-17)
+        This return is given if pcre_dfa_exec()  encounters  a  condition  item
+        that  uses  a back reference for the condition, or a test for recursion
+        in a specific group. These are not supported.
+          PCRE_ERROR_DFA_UMLIMIT    (-18)
+        This return is given if pcre_dfa_exec() is called with an  extra  block
+        that contains a setting of the match_limit field. This is not supported
+        (it is meaningless).
+          PCRE_ERROR_DFA_WSSIZE     (-19)
+        This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
+        workspace vector.
+          PCRE_ERROR_DFA_RECURSE    (-20)
+        When  a  recursive subpattern is processed, the matching function calls
+        itself recursively, using private vectors for  ovector  and  workspace.
+        This  error  is  given  if  the output vector is not large enough. This
+        should be extremely rare, as a vector of size 1000 is used.
- MATCHING A PATTERN
-      The function pcre_exec() is called to match a subject string
-      against  a pre-compiled pattern, which is passed in the code
-      argument. If the pattern has been studied, the result of the
-      study should be passed in the extra argument. Otherwise this
-      must be NULL.
-      The PCRE_ANCHORED option can be passed in the options  argu-
-      ment,  whose unused bits must be zero. However, if a pattern
-      was  compiled  with  PCRE_ANCHORED,  or  turned  out  to  be
-      anchored  by  virtue  of  its  contents,  it  cannot be made
-      unachored at matching time.
-      There are also three further options that can be set only at
-      matching time:
-        PCRE_NOTBOL
-      The first character of the string is not the beginning of  a
-      line,  so  the  circumflex  metacharacter  should  not match
-      before it. Setting this without PCRE_MULTILINE  (at  compile
-      time) causes circumflex never to match.
-        PCRE_NOTEOL
-      The end of the string is not the end of a line, so the  dol-
-      lar  metacharacter should not match it nor (except in multi-
-      line mode) a newline immediately  before  it.  Setting  this
-      without PCRE_MULTILINE (at compile time) causes dollar never
-      to match.
-        PCRE_NOTEMPTY
-      An empty string is not considered to be  a  valid  match  if
-      this  option  is  set. If there are alternatives in the pat-
-      tern, they are tried. If  all  the  alternatives  match  the
-      empty  string,  the  entire match fails. For example, if the
-      pattern
-        a?b?
-      is applied to a string not beginning with  "a"  or  "b",  it
-      matches  the  empty string at the start of the subject. With
-      PCRE_NOTEMPTY set, this match is not valid, so PCRE searches
-      further into the string for occurrences of "a" or "b".
-      Perl has no direct equivalent of PCRE_NOTEMPTY, but it  does
-      make  a  special case of a pattern match of the empty string
-      within its split() function, and when using the /g modifier.
-      It  is possible to emulate Perl's behaviour after matching a
-      null string by first trying the  match  again  at  the  same
-      offset  with  PCRE_NOTEMPTY  set,  and then if that fails by
-      advancing the starting offset  (see  below)  and  trying  an
-      ordinary match again.
-      The subject string is passed as  a  pointer  in  subject,  a
-      length  in  length,  and  a  starting offset in startoffset.
-      Unlike the pattern string, it may contain binary zero  char-
-      acters.  When  the starting offset is zero, the search for a
-      match starts at the beginning of the subject, and this is by
-      far the most common case.
-      A non-zero starting offset  is  useful  when  searching  for
-      another  match  in  the  same subject by calling pcre_exec()
-      again after a previous success.  Setting startoffset differs
-      from  just  passing  over  a  shortened  string  and setting
-      PCRE_NOTBOL in the case of a pattern that  begins  with  any
-      kind of lookbehind. For example, consider the pattern
-        \Biss\B
-      which finds occurrences of "iss" in the middle of words. (\B
-      matches only if the current position in the subject is not a
-      word boundary.) When applied to the string "Mississipi"  the
-      first  call  to  pcre_exec()  finds the first occurrence. If
-      pcre_exec() is called again with just the remainder  of  the
-      subject,  namely  "issipi", it does not match, because \B is
-      always false at the start of the subject, which is deemed to
-      be  a  word  boundary. However, if pcre_exec() is passed the
-      entire string again, but with startoffset set to 4, it finds
-      the  second  occurrence  of "iss" because it is able to look
-      behind the starting point to discover that it is preceded by
-      a letter.
-      If a non-zero starting offset is passed when the pattern  is
-      anchored, one attempt to match at the given offset is tried.
-      This can only succeed if the pattern does  not  require  the
-      match to be at the start of the subject.
-      In general, a pattern matches a certain portion of the  sub-
-      ject,  and  in addition, further substrings from the subject
-      may be picked out by parts of  the  pattern.  Following  the
-      usage  in  Jeffrey Friedl's book, this is called "capturing"
-      in what follows, and the phrase  "capturing  subpattern"  is
-      used for a fragment of a pattern that picks out a substring.
-      PCRE supports several other kinds of  parenthesized  subpat-
-      tern that do not cause substrings to be captured.
-      Captured substrings are returned to the caller via a  vector
-      of  integer  offsets whose address is passed in ovector. The
-      number of elements in the vector is passed in ovecsize.  The
-      first two-thirds of the vector is used to pass back captured
-      substrings, each substring using a  pair  of  integers.  The
-      remaining  third  of  the  vector  is  used  as workspace by
-      pcre_exec() while matching capturing subpatterns, and is not
-      available for passing back information. The length passed in
-      ovecsize should always be a multiple of three. If it is not,
-      it is rounded down.
-      When a match has been successful, information about captured
-      substrings is returned in pairs of integers, starting at the
-      beginning of ovector, and continuing up to two-thirds of its
-      length  at  the  most. The first element of a pair is set to
-      the offset of the first character in a  substring,  and  the
-      second is set to the offset of the first character after the
-      end of a substring. The first  pair,  ovector[0]  and  ovec-
-      tor[1],  identify  the portion of the subject string matched
-      by the entire pattern. The next pair is used for  the  first
-      capturing  subpattern,  and  so  on.  The  value returned by
-      pcre_exec() is the number of pairs that have  been  set.  If
-      there  are no capturing subpatterns, the return value from a
-      successful match is 1, indicating that just the  first  pair
-      of offsets has been set.
-      Some convenience functions are provided for  extracting  the
-      captured substrings as separate strings. These are described
-      in the following section.
-      It is possible for an capturing  subpattern  number  n+1  to
-      match  some  part  of  the subject when subpattern n has not
-      been used at all.  For  example,  if  the  string  "abc"  is
-      matched  against the pattern (a|(z))(bc) subpatterns 1 and 3
-      are matched, but 2 is not. When this  happens,  both  offset
-      values corresponding to the unused subpattern are set to -1.
-      If a capturing subpattern is matched repeatedly, it  is  the
-      last  portion  of  the  string  that  it  matched  that gets
-      returned.
-      If the vector is too small to hold  all  the  captured  sub-
-      strings,  it is used as far as possible (up to two-thirds of
-      its length), and the function returns a value  of  zero.  In
-      particular,  if  the  substring offsets are not of interest,
-      pcre_exec() may be called with ovector passed  as  NULL  and
-      ovecsize  as  zero.  However,  if  the pattern contains back
-      references and the ovector isn't big enough to remember  the
-      related  substrings,  PCRE  has to get additional memory for
-      use during matching. Thus it is usually advisable to  supply
-      an ovector.
-      Note that pcre_info() can be used to find out how many  cap-
-      turing  subpatterns  there  are  in  a compiled pattern. The
-      smallest size for ovector that will  allow  for  n  captured
-      substrings  in  addition  to  the  offsets  of the substring
-      matched by the whole pattern is (n+1)*3.
-      If pcre_exec() fails, it returns a negative number. The fol-
-      lowing are defined in the header file:
-        PCRE_ERROR_NOMATCH        (-1)
-      The subject string did not match the pattern.
-        PCRE_ERROR_NULL           (-2)
-      Either code or subject was passed as NULL,  or  ovector  was
-      NULL and ovecsize was not zero.
-        PCRE_ERROR_BADOPTION      (-3)
-      An unrecognized bit was set in the options argument.
-        PCRE_ERROR_BADMAGIC       (-4)
-      PCRE stores a 4-byte "magic number" at the start of the com-
-      piled  code,  to  catch  the  case  when it is passed a junk
-      pointer. This is the error it gives when  the  magic  number
-      isn't present.
-        PCRE_ERROR_UNKNOWN_NODE   (-5)
-      While running the pattern match, an unknown item was encoun-
-      tered in the compiled pattern. This error could be caused by
-      a bug in PCRE or by overwriting of the compiled pattern.
-        PCRE_ERROR_NOMEMORY       (-6)
-      If a pattern contains back references, but the ovector  that
-      is  passed  to pcre_exec() is not big enough to remember the
-      referenced substrings, PCRE gets a block of  memory  at  the
-      start  of  matching to use for this purpose. If the call via
-      pcre_malloc() fails, this error  is  given.  The  memory  is
-      freed at the end of matching.
- EXTRACTING CAPTURED SUBSTRINGS
-      Captured substrings can be accessed directly  by  using  the
-      offsets returned by pcre_exec() in ovector. For convenience,
-      the functions  pcre_copy_substring(),  pcre_get_substring(),
-      and  pcre_get_substring_list()  are  provided for extracting
-      captured  substrings  as  new,   separate,   zero-terminated
-      strings.   A  substring  that  contains  a  binary  zero  is
-      correctly extracted and has a further zero added on the end,
-      but the result does not, of course, function as a C string.
-      The first three arguments are the same for all  three  func-
-      tions:  subject  is  the  subject string which has just been
-      successfully matched, ovector is a pointer to the vector  of
-      integer   offsets   that  was  passed  to  pcre_exec(),  and
-      stringcount is the number of substrings that  were  captured
-      by  the  match,  including  the  substring  that matched the
-      entire regular expression. This is  the  value  returned  by
-      pcre_exec  if  it  is  greater  than  zero.  If  pcre_exec()
-      returned zero, indicating that it ran out of space in  ovec-
-      tor, then the value passed as stringcount should be the size
-      of the vector divided by three.
-      The functions pcre_copy_substring() and pcre_get_substring()
-      extract a single substring, whose number is given as string-
-      number. A value of zero extracts the substring that  matched
-      the entire pattern, while higher values extract the captured
-      substrings. For pcre_copy_substring(), the string is  placed
-      in  buffer,  whose  length is given by buffersize, while for
-      pcre_get_substring() a new block of store  is  obtained  via
-      pcre_malloc,  and its address is returned via stringptr. The
-      yield of the function is  the  length  of  the  string,  not
-      including the terminating zero, or one of
-        PCRE_ERROR_NOMEMORY       (-6)
-      The buffer was too small for pcre_copy_substring(),  or  the
-      attempt to get memory failed for pcre_get_substring().
-        PCRE_ERROR_NOSUBSTRING    (-7)
-      There is no substring whose number is stringnumber.
-      The pcre_get_substring_list() function extracts  all  avail-
-      able  substrings  and builds a list of pointers to them. All
-      this is done in a single block of memory which  is  obtained
-      via pcre_malloc. The address of the memory block is returned
-      via listptr, which is also the start of the list  of  string
-      pointers.  The  end of the list is marked by a NULL pointer.
-      The yield of the function is zero if all went well, or
-        PCRE_ERROR_NOMEMORY       (-6)
-      if the attempt to get the memory block failed.
-      When any of these functions encounter a  substring  that  is
-      unset, which can happen when capturing subpattern number n+1
-      matches some part of the subject, but subpattern n  has  not
-      been  used  at all, they return an empty string. This can be
-      distinguished  from  a  genuine  zero-length  substring   by
-      inspecting the appropriate offset in ovector, which is nega-
-      tive for unset substrings.
+ SEE ALSO
+        pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
+        tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
- LIMITATIONS
+ AUTHOR
-      There are some size limitations in PCRE but it is hoped that
-      they will never in practice be relevant.  The maximum length
-      of a compiled pattern is 65539 (sic) bytes.  All  values  in
-      repeating  quantifiers must be less than 65536.  The maximum
-      number of capturing subpatterns is 99.  The  maximum  number
-      of  all  parenthesized subpatterns, including capturing sub-
-      patterns, assertions, and other types of subpattern, is 200.
-      The maximum length of a subject string is the largest  posi-
-      tive number that an integer variable can hold. However, PCRE
-      uses recursion to handle subpatterns and indefinite  repeti-
-      tion.  This  means  that the available stack space may limit
-      the size of a subject string that can be processed  by  cer-
-      tain patterns.
- DIFFERENCES FROM PERL
-      The differences described here  are  with  respect  to  Perl
-.005.
-. By default, a whitespace character is any character  that
-      the  C  library  function isspace() recognizes, though it is
-      possible to compile PCRE  with  alternative  character  type
-      tables. Normally isspace() matches space, formfeed, newline,
-      carriage return, horizontal tab, and vertical tab. Perl 5 no
-      longer  includes vertical tab in its set of whitespace char-
-      acters. The \v escape that was in the Perl documentation for
-      a long time was never in fact recognized. However, the char-
-      acter itself was treated as whitespace at least up to 5.002.
-      In 5.004 and 5.005 it does not match \s.
-. PCRE does  not  allow  repeat  quantifiers  on  lookahead
-      assertions. Perl permits them, but they do not mean what you
-      might think. For example, (?!a){3} does not assert that  the
-      next  three characters are not "a". It just asserts that the
-      next character is not "a" three times.
-. Capturing subpatterns that occur inside  negative  looka-
-      head  assertions  are  counted,  but  their  entries  in the
-      offsets vector are never set. Perl sets its numerical  vari-
-      ables  from  any  such  patterns that are matched before the
-      assertion fails to match something (thereby succeeding), but
-      only  if  the negative lookahead assertion contains just one
-      branch.
-. Though binary zero characters are supported in  the  sub-
-      ject  string,  they  are  not  allowed  in  a pattern string
-      because it is passed as a normal  C  string,  terminated  by
-      zero. The escape sequence "\0" can be used in the pattern to
-      represent a binary zero.
-. The following Perl escape sequences  are  not  supported:
-      \l,  \u,  \L,  \U,  \E, \Q. In fact these are implemented by
-      Perl's general string-handling and are not part of its  pat-
-      tern matching engine.
-. The Perl \G assertion is  not  supported  as  it  is  not
-      relevant to single pattern matches.
-. Fairly obviously, PCRE does  not  support  the  (?{code})
-      construction.
-. There are at the time of writing some  oddities  in  Perl
-.005_02  concerned  with  the  settings of captured strings
-      when part of a pattern is repeated.  For  example,  matching
-      "aba"  against the pattern /^(a(b)?)+$/ sets $2 to the value
-      "b", but matching "aabbaa" against /^(aa(bb)?)+$/ leaves  $2
-      unset.    However,    if   the   pattern   is   changed   to
-      /^(aa(b(b))?)+$/ then $2 (and $3) get set.
-      In Perl 5.004 $2 is set in both cases, and that is also true
-      of PCRE. If in the future Perl changes to a consistent state
-      that is different, PCRE may change to follow.
-. Another as yet unresolved discrepancy  is  that  in  Perl
-.005_02  the  pattern /^(a)?(?(1)a|b)+$/ matches the string
-      "a", whereas in PCRE it does not.  However, in both Perl and
-      PCRE /^(a)?a/ matched against "a" leaves $1 unset.
-. PCRE  provides  some  extensions  to  the  Perl  regular
-      expression facilities:
-      (a) Although lookbehind assertions must match  fixed  length
-      strings,  each  alternative branch of a lookbehind assertion
-      can match a different length of string. Perl 5.005  requires
-      them all to have the same length.
-      (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is  not
-      set,  the  $ meta- character matches only at the very end of
-      the string.
-      (c) If PCRE_EXTRA is set, a backslash followed by  a  letter
-      with no special meaning is faulted.
-      (d)  If  PCRE_UNGREEDY  is  set,  the  greediness   of   the
-      repetition quantifiers is inverted, that is, by default they
-      are not greedy, but if followed by a question mark they are.
-      (e) PCRE_ANCHORED can be used to force a pattern to be tried
-      only at the start of the subject.
-      (f) The PCRE_NOTBOL, PCRE_NOTEOL, and PCRE_NOTEMPTY  options
-      for pcre_exec() have no Perl equivalents.
- REGULAR EXPRESSION DETAILS
-      The syntax and semantics of  the  regular  expressions  sup-
-      ported  by PCRE are described below. Regular expressions are
-      also described in the Perl documentation and in a number  of
-      other  books,  some  of which have copious examples. Jeffrey
-      Friedl's  "Mastering  Regular  Expressions",  published   by
-      O'Reilly  (ISBN 1-56592-257-3), covers them in great detail.
-      The description here is intended as reference documentation.
-      A regular expression is a pattern that is matched against  a
-      subject string from left to right. Most characters stand for
-      themselves in a pattern, and match the corresponding charac-
-      ters in the subject. As a trivial example, the pattern
-        The quick brown fox
-      matches a portion of a subject string that is  identical  to
-      itself.  The  power  of  regular  expressions comes from the
-      ability to include alternatives and repetitions in the  pat-
-      tern.  These  are encoded in the pattern by the use of meta-
-      characters, which do not stand for  themselves  but  instead
-      are interpreted in some special way.
-      There are two different sets of meta-characters: those  that
-      are  recognized anywhere in the pattern except within square
-      brackets, and those that are recognized in square  brackets.
-      Outside square brackets, the meta-characters are as follows:
-        \      general escape character with several uses
-        ^      assert start of  subject  (or  line,  in  multiline
-      mode)
-        $      assert end of subject (or line, in multiline mode)
-        .      match any character except newline (by default)
-        [      start character class definition
-        |      start of alternative branch
-        (      start subpattern
-        )      end subpattern
-        ?      extends the meaning of (
-               also 0 or 1 quantifier
-               also quantifier minimizer
-        *      0 or more quantifier
-        +      1 or more quantifier
-        {      start min/max quantifier
-      Part of a pattern that is in square  brackets  is  called  a
-      "character  class".  In  a  character  class  the only meta-
-      characters are:
-        \      general escape character
-        ^      negate the class, but only if the first character
-        -      indicates character range
-        ]      terminates the character class
-      The following sections describe  the  use  of  each  of  the
+        Philip Hazel
-      meta-characters.
+        University Computing Service
+        Cambridge CB2 3QH, England.
+ REVISION
- BACKSLASH
+        Last updated: 24 April 2007
-      The backslash character has several uses. Firstly, if it  is
+        Copyright (c) 1997-2007 University of Cambridge.
-      followed  by  a  non-alphameric character, it takes away any
+ ------------------------------------------------------------------------------
-      special  meaning  that  character  may  have.  This  use  of
-      backslash  as  an  escape  character applies both inside and
-      outside character classes.
-      For example, if you want to match a "*" character, you write
-      "\*" in the pattern. This applies whether or not the follow-
-      ing character would otherwise  be  interpreted  as  a  meta-
-      character,  so it is always safe to precede a non-alphameric
-      with "\" to specify that it stands for itself.  In  particu-
-      lar, if you want to match a backslash, you write "\\".
-      If a pattern is compiled with the PCRE_EXTENDED option, whi-
-      tespace in the pattern (other than in a character class) and
-      characters between a "#" outside a character class  and  the
-      next  newline  character  are ignored. An escaping backslash
-      can be used to include a whitespace or "#" character as part
-      of the pattern.
-      A second use of backslash provides a way  of  encoding  non-
-      printing  characters  in patterns in a visible manner. There
-      is no restriction on the appearance of non-printing  charac-
-      ters,  apart from the binary zero that terminates a pattern,
-      but when a pattern is being prepared by text editing, it  is
-      usually  easier to use one of the following escape sequences
-      than the binary character it represents:
-        \a     alarm, that is, the BEL character (hex 07)
-        \cx    "control-x", where x is any character
-        \e     escape (hex 1B)
-        \f     formfeed (hex 0C)
-        \n     newline (hex 0A)
-        \r     carriage return (hex 0D)
-             tab (hex 09)
-        \xhh   character with hex code hh
-        \ddd   character with octal code ddd, or backreference
-      The precise effect of "\cx" is as follows: if "x" is a lower
-      case  letter,  it  is converted to upper case. Then bit 6 of
-      the character (hex 40) is inverted.  Thus "\cz" becomes  hex
-A, but "\c{" becomes hex 3B, while "\c;" becomes hex 7B.
-      After "\x", up to two hexadecimal digits are  read  (letters
-      can be in upper or lower case).
-      After "\0" up to two further octal digits are read. In  both
-      cases,  if  there are fewer than two digits, just those that
-      are present are used. Thus the sequence "\0\x\07"  specifies
-      two binary zeros followed by a BEL character.  Make sure you
-      supply two digits after the initial zero  if  the  character
-      that follows is itself an octal digit.
-      The handling of a backslash followed by a digit other than 0
-      is  complicated.   Outside  a character class, PCRE reads it
-      and any following digits as a decimal number. If the  number
-      is  less  than  10, or if there have been at least that many
-      previous capturing left parentheses in the  expression,  the
-      entire  sequence is taken as a back reference. A description
-      of how this works is given later, following  the  discussion
-      of parenthesized subpatterns.
-      Inside a character  class,  or  if  the  decimal  number  is
-      greater  than  9 and there have not been that many capturing
-      subpatterns, PCRE re-reads up to three octal digits  follow-
-      ing  the  backslash,  and  generates  a single byte from the
-      least significant 8 bits of the value. Any subsequent digits
-      stand for themselves.  For example:
-        \040   is another way of writing a space
-        \40    is the same, provided there are fewer than 40
-                  previous capturing subpatterns
-        \7     is always a back reference
-        \11    might be a back reference, or another way of
-                  writing a tab
-        \011   is always a tab
-        \0113  is a tab followed by the character "3"
-        \113   is the character with octal code 113 (since there
-                  can be no more than 99 back references)
-        \377   is a byte consisting entirely of 1 bits
-        \81    is either a back reference, or a binary zero
-                  followed by the two characters "8" and "1"
-      Note that octal values of 100 or greater must not be  intro-
-      duced  by  a  leading zero, because no more than three octal
-      digits are ever read.
-      All the sequences that define a single  byte  value  can  be
-      used both inside and outside character classes. In addition,
-      inside a character class, the sequence "\b"  is  interpreted
-      as  the  backspace  character  (hex 08). Outside a character
-      class it has a different meaning (see below).
-      The third use of backslash is for specifying generic charac-
-      ter types:
-        \d     any decimal digit
-        \D     any character that is not a decimal digit
-        \s     any whitespace character
-        \S     any character that is not a whitespace character
-        \w     any "word" character
-        \W     any "non-word" character
-      Each pair of escape sequences partitions the complete set of
-      characters  into  two  disjoint  sets.  Any  given character
-      matches one, and only one, of each pair.
-      A "word" character is any letter or digit or the  underscore
-      character,  that  is,  any  character which can be part of a
-      Perl "word". The definition of letters and  digits  is  con-
-      trolled  by PCRE's character tables, and may vary if locale-
-      specific matching is  taking  place  (see  "Locale  support"
-      above). For example, in the "fr" (French) locale, some char-
-      acter codes greater than 128 are used for accented  letters,
-      and these are matched by \w.
-      These character type sequences can appear  both  inside  and
-      outside  character classes. They each match one character of
-      the appropriate type. If the current matching  point  is  at
-      the end of the subject string, all of them fail, since there
-      is no character to match.
-      The fourth use of backslash is  for  certain  simple  asser-
-      tions. An assertion specifies a condition that has to be met
-      at a particular point in  a  match,  without  consuming  any
-      characters  from  the subject string. The use of subpatterns
-      for more complicated  assertions  is  described  below.  The
-      backslashed assertions are
-        \b     word boundary
-        \B     not a word boundary
-        \A     start of subject (independent of multiline mode)
-        \Z     end of subject or newline at  end  (independent  of
-      multiline mode)
-        \z     end of subject (independent of multiline mode)
-      These assertions may not appear in  character  classes  (but
-      note that "\b" has a different meaning, namely the backspace
-      character, inside a character class).
-      A word boundary is a position in the  subject  string  where
-      the current character and the previous character do not both
-      match \w or \W (i.e. one matches \w and  the  other  matches
-      \W),  or the start or end of the string if the first or last
-      character matches \w, respectively.
-      The \A, \Z, and \z assertions differ  from  the  traditional
-      circumflex  and  dollar  (described below) in that they only
-      ever match at the very start and end of the subject  string,
-      whatever  options  are  set.  They  are  not affected by the
-      PCRE_NOTBOL or PCRE_NOTEOL options. If the startoffset argu-
-      ment  of  pcre_exec()  is  non-zero, \A can never match. The
-      difference between \Z and \z is that  \Z  matches  before  a
-      newline  that is the last character of the string as well as
-      at the end of the string, whereas \z  matches  only  at  the
-      end.
+ PCRECALLOUT(3)                                                  PCRECALLOUT(3)
- CIRCUMFLEX AND DOLLAR
-      Outside a character class, in the default matching mode, the
+ NAME
-      circumflex  character  is an assertion which is true only if
+        PCRE - Perl-compatible regular expressions
-      the current matching point is at the start  of  the  subject
-      string.  If  the startoffset argument of pcre_exec() is non-
-      zero, circumflex can never match. Inside a character  class,
-      circumflex has an entirely different meaning (see below).
-      Circumflex need not be the first character of the pattern if
-      a  number of alternatives are involved, but it should be the
-      first thing in each alternative in which it appears  if  the
-      pattern is ever to match that branch. If all possible alter-
-      natives start with a circumflex, that is, if the pattern  is
-      constrained to match only at the start of the subject, it is
-      said to be an "anchored" pattern. (There are also other con-
-      structs that can cause a pattern to be anchored.)
-      A dollar character is an assertion which is true only if the
-      current  matching point is at the end of the subject string,
-      or immediately before a newline character that is  the  last
-      character in the string (by default). Dollar need not be the
-      last character of the pattern if a  number  of  alternatives
-      are  involved,  but it should be the last item in any branch
-      in which it appears.  Dollar has no  special  meaning  in  a
-      character class.
-      The meaning of dollar can be changed so that it matches only
-      at   the   very   end   of   the   string,  by  setting  the
-      PCRE_DOLLAR_ENDONLY option at compile or matching time. This
-      does not affect the \Z assertion.
-      The meanings of the circumflex  and  dollar  characters  are
-      changed  if  the  PCRE_MULTILINE option is set. When this is
-      the case,  they  match  immediately  after  and  immediately
-      before an internal "\n" character, respectively, in addition
-      to matching at the start and end of the subject string.  For
-      example,  the  pattern  /^abc$/  matches  the subject string
-      "def\nabc" in multiline  mode,  but  not  otherwise.  Conse-
-      quently,  patterns  that  are  anchored  in single line mode
-      because all branches start with "^" are not anchored in mul-
-      tiline mode, and a match for circumflex is possible when the
-      startoffset  argument  of  pcre_exec()  is   non-zero.   The
-      PCRE_DOLLAR_ENDONLY  option  is ignored if PCRE_MULTILINE is
-      set.
-      Note that the sequences \A, \Z, and \z can be used to  match
-      the  start  and end of the subject in both modes, and if all
-      branches of a pattern start with \A is it  always  anchored,
-      whether PCRE_MULTILINE is set or not.
+ PCRE CALLOUTS
- FULL STOP (PERIOD, DOT)
+        int (*pcre_callout)(pcre_callout_block *);
-      Outside a character class, a dot in the pattern matches  any
-      one character in the subject, including a non-printing char-
-      acter, but not (by default)  newline.   If  the  PCRE_DOTALL
-      option  is  set,  then dots match newlines as well. The han-
-      dling of dot is entirely independent of the handling of cir-
-      cumflex  and  dollar,  the only relationship being that they
-      both involve newline characters.  Dot has no special meaning
-      in a character class.
- SQUARE BRACKETS
-      An opening square bracket introduces a character class, ter-
-      minated  by  a  closing  square  bracket.  A  closing square
-      bracket on its own is  not  special.  If  a  closing  square
-      bracket  is  required as a member of the class, it should be
-      the first data character in the class (after an initial cir-
-      cumflex, if present) or escaped with a backslash.
-      A character class matches a single character in the subject;
-      the  character  must  be in the set of characters defined by
-      the class, unless the first character in the class is a cir-
-      cumflex,  in which case the subject character must not be in
-      the set defined by the class. If a  circumflex  is  actually
-      required  as  a  member  of  the class, ensure it is not the
-      first character, or escape it with a backslash.
-      For example, the character class [aeiou] matches  any  lower
-      case vowel, while [^aeiou] matches any character that is not
-      a lower case vowel. Note that a circumflex is  just  a  con-
-      venient  notation for specifying the characters which are in
-      the class by enumerating those that are not. It  is  not  an
-      assertion:  it  still  consumes a character from the subject
-      string, and fails if the current pointer is at  the  end  of
-      the string.
-      When caseless matching  is  set,  any  letters  in  a  class
-      represent  both their upper case and lower case versions, so
-      for example, a caseless [aeiou] matches "A" as well as  "a",
-      and  a caseless [^aeiou] does not match "A", whereas a case-
-      ful version would.
-      The newline character is never treated in any special way in
-      character  classes,  whatever the setting of the PCRE_DOTALL
-      or PCRE_MULTILINE options is. A  class  such  as  [^a]  will
-      always match a newline.
-      The minus (hyphen) character can be used to specify a  range
-      of  characters  in  a  character  class.  For example, [d-m]
-      matches any letter between d and m, inclusive.  If  a  minus
-      character  is required in a class, it must be escaped with a
-      backslash or appear in a position where it cannot be  inter-
-      preted as indicating a range, typically as the first or last
-      character in the class.
-      It is not possible to have the literal character "]" as  the
-      end  character  of  a  range.  A  pattern such as [W-]46] is
-      interpreted as a class of two characters ("W" and "-")  fol-
-      lowed by a literal string "46]", so it would match "W46]" or
-      "-46]". However, if the "]" is escaped with a  backslash  it
-      is  interpreted  as  the end of range, so [W-\]46] is inter-
-      preted as a single class containing a range followed by  two
-      separate characters. The octal or hexadecimal representation
-      of "]" can also be used to end a range.
-      Ranges operate in ASCII collating sequence. They can also be
-      used  for  characters  specified  numerically,  for  example
-      [\000-\037]. If a range that includes letters is  used  when
-      caseless  matching  is set, it matches the letters in either
-      case. For example, [W-c] is equivalent  to  [][\^_`wxyzabc],
-      matched  caselessly,  and  if  character tables for the "fr"
-      locale are in use, [\xc8-\xcb] matches accented E characters
-      in both cases.
-      The character types \d, \D, \s, \S,  \w,  and  \W  may  also
-      appear  in  a  character  class, and add the characters that
-      they match to the class. For example, [\dABCDEF] matches any
-      hexadecimal  digit.  A  circumflex  can conveniently be used
-      with the upper case character types to specify a  more  res-
-      tricted set of characters than the matching lower case type.
-      For example, the class [^\W_] matches any letter  or  digit,
-      but not underscore.
-      All non-alphameric characters other than \,  -,  ^  (at  the
-      start)  and  the  terminating ] are non-special in character
-      classes, but it does no harm if they are escaped.
+        PCRE provides a feature called "callout", which is a means of temporar-
+        ily passing control to the caller of PCRE  in  the  middle  of  pattern
+        matching.  The  caller of PCRE provides an external function by putting
+        its entry point in the global variable pcre_callout. By  default,  this
+        variable contains NULL, which disables all calling out.
+        Within  a  regular  expression,  (?C) indicates the points at which the
+        external function is to be called.  Different  callout  points  can  be
+        identified  by  putting  a number less than 256 after the letter C. The
+        default value is zero.  For  example,  this  pattern  has  two  callout
+        points:
+          (?C1)abc(?C2)def
+        If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
+        called, PCRE automatically  inserts  callouts,  all  with  number  255,
+        before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is
+        used with the pattern
+          A(\d{2}|--)
+        it is processed as if it were
+        (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
+        Notice that there is a callout before and after  each  parenthesis  and
+        alternation  bar.  Automatic  callouts  can  be  used  for tracking the
+        progress of pattern matching. The pcretest command has an  option  that
+        sets  automatic callouts; when it is used, the output indicates how the
+        pattern is matched. This is useful information when you are  trying  to
+        optimize the performance of a particular pattern.
+ MISSING CALLOUTS
+        You  should  be  aware  that,  because of optimizations in the way PCRE
+        matches patterns, callouts sometimes do not happen. For example, if the
+        pattern is
+          ab(?C4)cd
+        PCRE knows that any matching string must contain the letter "d". If the
+        subject string is "abyz", the lack of "d" means that  matching  doesn't
+        ever  start,  and  the  callout is never reached. However, with "abyd",
+        though the result is still no match, the callout is obeyed.
+ THE CALLOUT INTERFACE
+        During matching, when PCRE reaches a callout point, the external  func-
+        tion  defined by pcre_callout is called (if it is set). This applies to
+        both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
+        only  argument  to  the callout function is a pointer to a pcre_callout
+        block. This structure contains the following fields:
+          int          version;
+          int          callout_number;
+          int         *offset_vector;
+          const char  *subject;
+          int          subject_length;
+          int          start_match;
+          int          current_position;
+          int          capture_top;
+          int          capture_last;
+          void        *callout_data;
+          int          pattern_position;
+          int          next_item_length;
+        The version field is an integer containing the version  number  of  the
+        block  format. The initial version was 0; the current version is 1. The
+        version number will change again in future  if  additional  fields  are
+        added, but the intention is never to remove any of the existing fields.
+        The callout_number field contains the number of the  callout,  as  com-
+        piled  into  the pattern (that is, the number after ?C for manual call-
+        outs, and 255 for automatically generated callouts).
+        The offset_vector field is a pointer to the vector of offsets that  was
+        passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When
+        pcre_exec() is used, the contents can be inspected in order to  extract
+        substrings  that  have  been  matched  so  far,  in the same way as for
+        extracting substrings after a match has completed. For  pcre_dfa_exec()
+        this field is not useful.
+        The subject and subject_length fields contain copies of the values that
+        were passed to pcre_exec().
+        The start_match field contains the offset within the subject  at  which
+        the  current match attempt started. If the pattern is not anchored, the
+        callout function may be called several times from the same point in the
+        pattern for different starting points in the subject.
+        The  current_position  field  contains the offset within the subject of
+        the current match pointer.
+        When the pcre_exec() function is used, the capture_top  field  contains
+        one  more than the number of the highest numbered captured substring so
+        far. If no substrings have been captured, the value of  capture_top  is
+        one.  This  is always the case when pcre_dfa_exec() is used, because it
+        does not support captured substrings.
+        The capture_last field contains the number of the  most  recently  cap-
+        tured  substring. If no substrings have been captured, its value is -1.
+        This is always the case when pcre_dfa_exec() is used.
+        The callout_data field contains a value that is passed  to  pcre_exec()
+        or  pcre_dfa_exec() specifically so that it can be passed back in call-
+        outs. It is passed in the pcre_callout field  of  the  pcre_extra  data
+        structure.  If  no such data was passed, the value of callout_data in a
+        pcre_callout block is NULL. There is a description  of  the  pcre_extra
+        structure in the pcreapi documentation.
+        The  pattern_position field is present from version 1 of the pcre_call-
+        out structure. It contains the offset to the next item to be matched in
+        the pattern string.
+        The  next_item_length field is present from version 1 of the pcre_call-
+        out structure. It contains the length of the next item to be matched in
+        the  pattern  string. When the callout immediately precedes an alterna-
+        tion bar, a closing parenthesis, or the end of the pattern, the  length
+        is  zero.  When the callout precedes an opening parenthesis, the length
+        is that of the entire subpattern.
+        The pattern_position and next_item_length fields are intended  to  help
+        in  distinguishing between different automatic callouts, which all have
+        the same callout number. However, they are set for all callouts.
+ RETURN VALUES
+        The external callout function returns an integer to PCRE. If the  value
+        is  zero,  matching  proceeds  as  normal. If the value is greater than
+        zero, matching fails at the current point, but  the  testing  of  other
+        matching possibilities goes ahead, just as if a lookahead assertion had
+        failed. If the value is less than zero, the  match  is  abandoned,  and
+        pcre_exec() (or pcre_dfa_exec()) returns the negative value.
+        Negative   values   should   normally   be   chosen  from  the  set  of
+        PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
+        dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is
+        reserved for use by callout functions; it will never be  used  by  PCRE
+        itself.
- VERTICAL BAR
+ AUTHOR
-      Vertical bar characters are  used  to  separate  alternative
-      patterns. For example, the pattern
-        gilbert|sullivan
+        Philip Hazel
+        University Computing Service
+        Cambridge CB2 3QH, England.
-      matches either "gilbert" or "sullivan". Any number of alter-
-      natives  may  appear,  and an empty alternative is permitted
-      (matching the empty string).   The  matching  process  tries
-      each  alternative in turn, from left to right, and the first
-      one that succeeds is used. If the alternatives are within  a
-      subpattern  (defined  below),  "succeeds" means matching the
-      rest of the main pattern as well as the alternative  in  the
-      subpattern.
+ REVISION
+        Last updated: 06 March 2007
+        Copyright (c) 1997-2007 University of Cambridge.
+ ------------------------------------------------------------------------------
- INTERNAL OPTION SETTING
-      The settings of PCRE_CASELESS, PCRE_MULTILINE,  PCRE_DOTALL,
-      and  PCRE_EXTENDED can be changed from within the pattern by
-      a sequence of Perl option letters enclosed between "(?"  and
-      ")". The option letters are
-        i  for PCRE_CASELESS
-        m  for PCRE_MULTILINE
-        s  for PCRE_DOTALL
-        x  for PCRE_EXTENDED
-      For example, (?im) sets caseless, multiline matching. It  is
-      also possible to unset these options by preceding the letter
-      with a hyphen, and a combined setting and unsetting such  as
-      (?im-sx),  which sets PCRE_CASELESS and PCRE_MULTILINE while
-      unsetting PCRE_DOTALL and PCRE_EXTENDED, is also  permitted.
-      If  a  letter  appears both before and after the hyphen, the
-      option is unset.
-      The scope of these option changes depends on  where  in  the
-      pattern  the  setting  occurs. For settings that are outside
-      any subpattern (defined below), the effect is the same as if
-      the  options were set or unset at the start of matching. The
-      following patterns all behave in exactly the same way:
-        (?i)abc
-        a(?i)bc
-        ab(?i)c
-        abc(?i)
-      which in turn is the same as compiling the pattern abc  with
-      PCRE_CASELESS  set.   In  other words, such "top level" set-
-      tings apply to the whole pattern  (unless  there  are  other
-      changes  inside subpatterns). If there is more than one set-
-      ting of the same option at top level, the rightmost  setting
-      is used.
-      If an option change occurs inside a subpattern,  the  effect
-      is  different.  This is a change of behaviour in Perl 5.005.
-      An option change inside a subpattern affects only that  part
-      of the subpattern that follows it, so
-        (a(?i)b)c
-      matches  abc  and  aBc  and  no  other   strings   (assuming
-      PCRE_CASELESS  is  not used).  By this means, options can be
-      made to have different settings in different  parts  of  the
-      pattern.  Any  changes  made  in one alternative do carry on
-      into subsequent branches within  the  same  subpattern.  For
-      example,
-        (a(?i)b|c)
-      matches "ab", "aB", "c", and "C", even though when  matching
-      "C" the first branch is abandoned before the option setting.
-      This is because the effects of  option  settings  happen  at
-      compile  time. There would be some very weird behaviour oth-
-      erwise.
-      The PCRE-specific options PCRE_UNGREEDY and  PCRE_EXTRA  can
-      be changed in the same way as the Perl-compatible options by
-      using the characters U and X  respectively.  The  (?X)  flag
-      setting  is  special in that it must always occur earlier in
-      the pattern than any of the additional features it turns on,
-      even when it is at top level. It is best put at the start.
+ PCRECOMPAT(3)                                                    PCRECOMPAT(3)
- SUBPATTERNS
+ NAME
-      Subpatterns are delimited by parentheses  (round  brackets),
+        PCRE - Perl-compatible regular expressions
-      which can be nested.  Marking part of a pattern as a subpat-
-      tern does two things:
-. It localizes a set of alternatives. For example, the pat-
-      tern
-        cat(aract|erpillar|)
-      matches one of the words "cat",  "cataract",  or  "caterpil-
-      lar".  Without  the  parentheses, it would match "cataract",
-      "erpillar" or the empty string.
-. It sets up the subpattern as a capturing  subpattern  (as
-      defined  above).   When the whole pattern matches, that por-
-      tion of the subject string that matched  the  subpattern  is
-      passed  back  to  the  caller  via  the  ovector argument of
-      pcre_exec(). Opening parentheses are counted  from  left  to
-      right (starting from 1) to obtain the numbers of the captur-
-      ing subpatterns.
-      For example, if the string "the red king" is matched against
-      the pattern
-        the ((red|white) (king|queen))
-      the captured substrings are "red king", "red",  and  "king",
-      and are numbered 1, 2, and 3.
-      The fact that plain parentheses fulfil two functions is  not
-      always  helpful.  There are often times when a grouping sub-
-      pattern is required without a capturing requirement.  If  an
-      opening parenthesis is followed by "?:", the subpattern does
-      not do any capturing, and is not counted when computing  the
-      number of any subsequent capturing subpatterns. For example,
-      if the string "the white queen" is matched against the  pat-
-      tern
-        the ((?:red|white) (king|queen))
-      the captured substrings are "white queen" and  "queen",  and
-      are  numbered  1  and 2. The maximum number of captured sub-
-      strings is 99, and the maximum number  of  all  subpatterns,
-      both capturing and non-capturing, is 200.
-      As a  convenient  shorthand,  if  any  option  settings  are
-      required  at  the  start  of a non-capturing subpattern, the
-      option letters may appear between the "?" and the ":".  Thus
-      the two patterns
-        (?i:saturday|sunday)
-        (?:(?i)saturday|sunday)
-      match exactly the same set of strings.  Because  alternative
-      branches  are  tried from left to right, and options are not
-      reset until the end of the subpattern is reached, an  option
-      setting  in  one  branch does affect subsequent branches, so
-      the above patterns match "SUNDAY" as well as "Saturday".
+ DIFFERENCES BETWEEN PCRE AND PERL
- REPETITION
+        This  document describes the differences in the ways that PCRE and Perl
-      Repetition is specified by quantifiers, which can follow any
+        handle regular expressions. The differences described here  are  mainly
-      of the following items:
+        with  respect  to  Perl 5.8, though PCRE version 7.0 contains some fea-
+        tures that are expected to be in the forthcoming Perl 5.10.
+. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details
+        of  what  it does have are given in the section on UTF-8 support in the
+        main pcre page.
+. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
+        permits  them,  but they do not mean what you might think. For example,
+        (?!a){3} does not assert that the next three characters are not "a". It
+        just asserts that the next character is not "a" three times.
+.  Capturing  subpatterns  that occur inside negative lookahead asser-
+        tions are counted, but their entries in the offsets  vector  are  never
+        set.  Perl sets its numerical variables from any such patterns that are
+        matched before the assertion fails to match something (thereby succeed-
+        ing),  but  only  if the negative lookahead assertion contains just one
+        branch.
+. Though binary zero characters are supported in the  subject  string,
+        they are not allowed in a pattern string because it is passed as a nor-
+        mal C string, terminated by zero. The escape sequence \0 can be used in
+        the pattern to represent a binary zero.
+.  The  following Perl escape sequences are not supported: \l, \u, \L,
+        \U, and \N. In fact these are implemented by Perl's general string-han-
+        dling  and are not part of its pattern matching engine. If any of these
+        are encountered by PCRE, an error is generated.
+. The Perl escape sequences \p, \P, and \X are supported only if  PCRE
+        is  built  with Unicode character property support. The properties that
+        can be tested with \p and \P are limited to the general category  prop-
+        erties  such  as  Lu and Nd, script names such as Greek or Han, and the
+        derived properties Any and L&.
+. PCRE does support the \Q...\E escape for quoting substrings. Charac-
+        ters  in  between  are  treated as literals. This is slightly different
+        from Perl in that $ and @ are  also  handled  as  literals  inside  the
+        quotes.  In Perl, they cause variable interpolation (but of course PCRE
+        does not have variables). Note the following examples:
+            Pattern            PCRE matches      Perl matches
+            \Qabc$xyz\E        abc$xyz           abc followed by the
+                                                   contents of $xyz
+            \Qabc\$xyz\E       abc\$xyz          abc\$xyz
+            \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
+        The \Q...\E sequence is recognized both inside  and  outside  character
+        classes.
+. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
+        constructions. However, there is support for recursive  patterns.  This
+        is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE
+        "callout" feature allows an external function to be called during  pat-
+        tern matching. See the pcrecallout documentation for details.
+.  Subpatterns  that  are  called  recursively or as "subroutines" are
+        always treated as atomic groups in  PCRE.  This  is  like  Python,  but
+        unlike Perl.
+.  There are some differences that are concerned with the settings of
+        captured strings when part of  a  pattern  is  repeated.  For  example,
+        matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
+        unset, but in PCRE it is set to "b".
+. PCRE provides some extensions to the Perl regular expression facil-
+        ities.   Perl  5.10  will  include new features that are not in earlier
+        versions, some of which (such as named parentheses) have been  in  PCRE
+        for some time. This list is with respect to Perl 5.10:
+        (a)  Although  lookbehind  assertions  must match fixed length strings,
+        each alternative branch of a lookbehind assertion can match a different
+        length of string. Perl requires them all to have the same length.
+        (b)  If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
+        meta-character matches only at the very end of the string.
+        (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
+        cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is
+        ignored. (Perl can be made to issue a warning.)
+        (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
+        fiers is inverted, that is, by default they are not greedy, but if fol-
+        lowed by a question mark they are.
+        (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
+        tried only at the first matching position in the subject string.
+        (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-
+        TURE options for pcre_exec() have no Perl equivalents.
+        (g) The callout facility is PCRE-specific.
+        (h) The partial matching facility is PCRE-specific.
-        a single character, possibly escaped
+        (i) Patterns compiled by PCRE can be saved and re-used at a later time,
-        the . metacharacter
+        even on different hosts that have the other endianness.
-        a character class
-        a back reference (see next section)
-        a parenthesized subpattern (unless it is  an  assertion  -
-      see below)
-      The general repetition quantifier specifies  a  minimum  and
-      maximum  number  of  permitted  matches,  by  giving the two
-      numbers in curly brackets (braces), separated  by  a  comma.
-      The  numbers  must be less than 65536, and the first must be
-      less than or equal to the second. For example:
-        z{2,4}
-      matches "zz", "zzz", or "zzzz". A closing brace on  its  own
-      is not a special character. If the second number is omitted,
-      but the comma is present, there is no upper  limit;  if  the
-      second number and the comma are both omitted, the quantifier
-      specifies an exact number of required matches. Thus
-        [aeiou]{3,}
-      matches at least 3 successive vowels,  but  may  match  many
-      more, while
-        \d{8}
-      matches exactly 8 digits.  An  opening  curly  bracket  that
-      appears  in a position where a quantifier is not allowed, or
-      one that does not match the syntax of a quantifier, is taken
-      as  a literal character. For example, {,6} is not a quantif-
-      ier, but a literal string of four characters.
-      The quantifier {0} is permitted, causing the  expression  to
-      behave  as  if the previous item and the quantifier were not
-      present.
       For c