PCRE2LIMITS(3)         FreeBSD Library Functions Manual         PCRE2LIMITS(3)

NAME
       PCRE2 - Perl-compatible regular expressions (revised API)

SIZE AND OTHER LIMITATIONS
       There are some size limitations in PCRE2 but it is hoped that they will
       never in practice be relevant.

       The maximum size of a compiled pattern is approximately 64 thousand
       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
       README file in the source distribution and the pcre2build 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.

       The maximum length of a source pattern string is essentially unlimited;
       it is the largest number a PCRE2_SIZE variable can hold. However, the
       program that calls pcre2_compile() can specify a smaller limit.

       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.

       All values in repeating quantifiers must be less than 65536.

       The maximum length of a lookbehind assertion is 65535 characters.

       There is no limit to the number of parenthesized groups, but there can
       be no more than 65535 capture groups, and there is 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
       default limit can be specified when PCRE2 is built; if not, the default
       is set to 250. An application can change this limit by calling
       pcre2_set_parens_nest_limit() to set the limit in a compile context.

       The maximum length of name for a named capture group is 32 code units,
       and the maximum number of such groups is 10000.

       The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or
       (*THEN) verb is 255 code units for the 8-bit library and 65535 code
       units for the 16-bit and 32-bit libraries.

       The maximum length of a string argument to a callout is the largest
       number a 32-bit unsigned integer can hold.

AUTHOR
       Philip Hazel
       University Computing Service
       Cambridge, England.

REVISION
       Last updated: 02 February 2019
       Copyright (c) 1997-2019 University of Cambridge.

PCRE2 10.33                    03 February 2019                 PCRE2LIMITS(3)