Added bundled PCRE2 library.

pcre2/doc/pcre2limits.3

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+.TH PCRE2LIMITS 3 "25 November 2014" "PCRE2 10.00"
+.SH NAME
+PCRE2 - Perl-compatible regular expressions (revised API)
+.SH "SIZE AND OTHER LIMITATIONS"
+.rs
+.sp
+There are some size limitations in PCRE2 but it is hoped that they will never
+in practice be relevant.
+.P
+The maximum size of a compiled pattern is approximately 64K code units for the
+8-bit and 16-bit libraries if PCRE2 is compiled with the default internal
+linkage size, which is 2 bytes for these libraries. If you want to process
+regular expressions that are truly enormous, you can compile PCRE2 with an
+internal linkage size of 3 or 4 (when building the 16-bit library, 3 is rounded
+up to 4). See the \fBREADME\fP file in the source distribution and the
+.\" HREF
+\fBpcre2build\fP
+.\"
+documentation for details. In these cases the limit is substantially larger.
+However, the speed of execution is slower. In the 32-bit library, the internal
+linkage size is always 4.
+.P
+The maximum length (in code units) of a subject string is one less than the
+largest number a PCRE2_SIZE variable can hold. PCRE2_SIZE is an unsigned
+integer type, usually defined as size_t. Its maximum value (that is
+~(PCRE2_SIZE)0) is reserved as a special indicator for zero-terminated strings
+and unset offsets.
+.P
+Note that when using the traditional matching function, PCRE2 uses recursion to
+handle subpatterns and indefinite 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
+.\" HREF
+\fBpcre2stack\fP
+.\"
+documentation.
+.P
+All values in repeating quantifiers must be less than 65536.
+.P
+There is no limit to the number of parenthesized subpatterns, but there can be
+no more than 65535 capturing subpatterns. There is, however, a limit to the
+depth of nesting of parenthesized subpatterns of all kinds. This is imposed in
+order to limit the amount of system stack used at compile time. The limit can
+be specified when PCRE2 is built; the default is 250.
+.P
+There is a limit to the number of forward references to subsequent subpatterns
+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.
+.P
+The maximum length of name for a named subpattern is 32 code units, and the
+maximum number of named subpatterns is 10000.
+.P
+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 and 32-bit libraries.
+.
+.
+.SH AUTHOR
+.rs
+.sp
+.nf
+Philip Hazel
+University Computing Service
+Cambridge, England.
+.fi
+.
+.
+.SH REVISION
+.rs
+.sp
+.nf
+Last updated: 25 November 2014
+Copyright (c) 1997-2014 University of Cambridge.
+.fi