my $g = {
  space			=> qr/\x20+/o,
  trailing_space	=> qr/\x20*/o,
};

my $irc_regex = qr/^
  (?:
    \x3a                #  : comes before hand
    (\S+)               #  [prefix]
    $g->{'space'}       #  Followed by a space
  )?                    # but is optional.
  (
    \d{3}|[a-zA-Z]+     #  [command]
  )                     # required.
  (?:
    $g->{'space'}       # Strip leading space off [middle]s
    (                   # [middle]s
      (?:
        [^\x00\x0a\x0d\x20\x3a]
        [^\x00\x0a\x0d\x20]*
      )                 # Match on 1 of these,
      (?:
        $g->{'space'}
        [^\x00\x0a\x0d\x20\x3a]
        [^\x00\x0a\x0d\x20]*
      ){0,13}           # then match on 0-13 of these,
    )
  )?                    # otherwise dont match at all.
  (?:
    $g->{'space'}\x3a   # Strip off leading spacecolon for [trailing]
    ([^\x00\x0a\x0d]*)	# [trailing]
  )?                    # [trailing] is not necessary.
  $g->{'trailing_space'}
$/x;