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  approximately  64K  data
       units  (bytes  for  the  8-bit  library,  16-bit  units  for the 16-bit
       library) if PCRE is compiled with the default internal linkage size  of
       2  bytes.  If  you  want  to process regular expressions that are truly
       enormous, you can compile PCRE with an internal linkage size of 3 or  4
       (when  building  the  16-bit  library,  3  is rounded up to 4). See the
       README file in the source distribution and the pcrebuild  documentation
       for  details.  In  these cases the limit is substantially larger.  How-
       ever, the speed of execution is slower.

       All values in repeating quantifiers must be less than 65536.

       There is no limit to the number of parenthesized subpatterns, but there
       can be no more than 65535 capturing subpatterns.

       There is a limit to the number of forward references to subsequent sub-
       patterns of around 200,000.  Repeated  forward  references  with  fixed
       upper  limits,  for example, (?2){0,100} when subpattern number 2 is to
       the right, are included in the count. There is no limit to  the  number
       of backward references.

       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  name  in  a  (*MARK),  (*PRUNE),  (*SKIP),  or
       (*THEN)  verb  is  255  for  the 8-bit library and 65535 for the 16-bit

       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.


       Philip Hazel
       University Computing Service
       Cambridge CB2 3QH, England.


       Last updated: 04 May 2012
       Copyright (c) 1997-2012 University of Cambridge.
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