$constraint =~ m@
   ^\s*        # skip all whitespace at beginning
   (
       /.+/            # capture the custom regex
       |m(.).+\2    # does this capture the ops? What does the |m do? why is the (.) and \2 in there?
   )
   [cgimosx]*    # ?? don't understand what this is for. what are we trying to match? I thought the ops were matched above
   \s*$        # skip all whitespace at end
   @x