the CS concept of regular expressions is not the same as the as implemented perl-compatable-regular-expression engine or posix regex which is what 99.9% of references to regular expressions are.

They are not any more a fundamental CS concept than the syntax of the C language is, or unicode encoding.

PCRE/posix regex arn't even regular expressions in CS terms (due to stuff like backreferences, and in the case of PCRE even turing completeness).