I'm not absolutely sure this isn't a joke that got out-of-hand. This is the COBOL of regular expressions. :)

Whilst the conventional regular expression syntax is arguably overly compact, this is just too far in the opposite direction!

Something more PEG-like, or even Perl 6 regex-like, would make more more readable regular expressions whilst not completely throwing out everything we think things mean. Hell, even /x -- ignore whitespace and comments -- can make things much clearer:

    / ^
      [0-9a-z._%+-]+           # The local part. Mailbox/user name. Can't contain ~, amongst other valid characters.
      \@
      [0-9a-z.-]+ \. [a-z]{2,} # The domain name. We've decided a TLD can never contain a digit, apparently.
    $ /x

Tangentally, there's no point validating email addresses with anything more complicated than /@/. If people want to enter an email address that doesn't work, they can and will. If you want to be sure that the address is valid, send it an email!