Even this is unnecessary. I'd say 99% of people using PCRE-like regexes have never read the documentation and realized `(?x)` exists.

We can write the regex like this, including all whitespace:

    (?x)
    ^\w+            # mandatory leading letters
    ( [-+.'] \w+ )* # optional suffix
    @
    \w+             # domain
    ( [-.] \w+ )*   # domain suffix
    ( \.\w+ ( [-.] \w+ )* )* #tld
    $

Also, btw, I hope no one is really using this regex. It's wrong; for example it appears to be deliberately designed to fail on IDNs.