You put an (s) in parentheses and it means cat or maybe cool cats. You put a ? question mark and it means are the cats cool? You put (cats?) and a question mark in parentheses and you wonder whether there are any cats. And if you put cat(s?) and s-question-mark then you think there's either one cat or numerous cats. Dig? (?)

{ (s)cat(s?) cool (cat)s }(?(?))