MDEV-4425 REGEXP enhancements

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+.TH PCRELIMITS 3 "24 June 2012" "PCRE 8.30"
+.SH NAME
+PCRE - Perl-compatible regular expressions
+.SH "SIZE AND OTHER LIMITATIONS"
+.rs
+.sp
+There are some size limitations in PCRE but it is hoped that they will never in
+practice be relevant.
+.P
+The maximum length of a compiled pattern is approximately 64K data units (bytes
+for the 8-bit library, 32-bit units for the 32-bit library, and 32-bit units for
+the 32-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 or 32-bit library, 3 is rounded up to 4). See the \fBREADME\fP file in
+the source distribution and the
+.\" HREF
+\fBpcrebuild\fP
+.\"
+documentation for details. In these cases the limit is substantially larger.
+However, the speed of execution is slower.
+.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.
+.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 characters, 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 library.
+.P
+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 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
+\fBpcrestack\fP
+.\"
+documentation.
+.
+.
+.SH AUTHOR
+.rs
+.sp
+.nf
+Philip Hazel
+University Computing Service
+Cambridge CB2 3QH, England.
+.fi
+.
+.
+.SH REVISION
+.rs
+.sp
+.nf
+Last updated: 04 May 2012
+Copyright (c) 1997-2012 University of Cambridge.
+.fi