I do not have the time or inclination to go through all these regex proposals in detail.
However, I am deeply, deeply opposed to Perl-style regular expression. They are fundamentally incompatible with Swift’s goal of clarity at the point of use.
Swift is an opinionated language, and it has chosen clarity. Perl-style regex literals are antithetical to that. We cannot, must not, absolutely should not sacrifice Swift’s clarity for them.
Perl-style regular expressions are a terrible syntax. They are illegible, incomprehensible, and aggressively unwelcoming. We need to proactively and vigilantly ensure that they do not enter the Swift language.