Unsupported regex features

Rax does not implement all the PCRE2 and Perl features. The following are not implemented for Rax regex relative to PCRE2 and Perl:

Table 9.1. PCRE2/Perl regex features not supported in Rax

SyntaxFunction
$<name|num> substitution like: $aap, $1, $&, $`, and $'.
(?<options> for the options a, d, l, u, m, s, and x
(?^Shorthand for a number of flags.
(?|Reset group numbering on |.
(?=Zero width match.
(?!Zero width non-match.
(?<=Zero width look behind match.
(?<!Zero width look behind non-match.
(?{Execute code.
(??{Execute code.
(?0Recursive group matching of the whole regex.
(?RRecursive group matching of the whole regex.
(? Recursive group matching by number.
(?-Recursive group matching by relative number.
(?+Recursive group matching by relative number.
(?&<name>Recursive group matching by name.
(?P><name>Recursive group matching by name.
(?(IIF for matched groups, code, etc.
(?>Independent subexpression.
(?[ Alternative class spec with logic operators an \p{}.