Hello! Thanks for the reply - you are probably right, and I accept that it's normal. However, there may be numerous frameworks getting built on the concept of collaboratively contributed regexes.

(Python likes prototyping, prototyping likes portable programming constructs, regular expressions are portable, for this and other factors and as past practice suggests, these will be a temptingly plausible choice as a basis for frameworks, etc.)

So I do accept it's normal (I haven't been deeply into regexes for cca 10 years, but I vaguely recall what's complex depends a lot on the type of engine, maybe A or B? pass on that one).

However people make mistakes that attackers seek...

(Not to lose that point, I am otherwise okay to let it go as "not a bug" if you're certain! I guess something should be done though.)