Damian Conway's https://metacpan.org/pod/PPR module defines a regex (in the commonly used sense) that can match perl source code - including perl regexes!
Edit: "The PPR module provides a single regular expression that defines a set of independent subpatterns suitable for matching entire Perl documents, as well as a wide range of individual syntactic components of Perl (i.e. statements, expressions, control blocks, variables, etc.)"
symantics vs. non-semantics. Perhaps examples/explainations of where regular expressions sit relative to grammars, grammar validation, syntax, and parsing might be helpful. [0][1][2][3][4]
https://stackoverflow.com/questions/49650847/determine-if-st...
The answer is yes, they’re regular. :-D