Input              Output
        ---------------------------------------
        'x|xy'             'xy?'
        'xx|xyx'           'xy?x'
        'a|abc'            'a(bc)?'
        'a|ab|abc'         'a(b(c)?)?'
        'a1|a2|a3'         'a[123]'

##</code><code>##

        /that|this|thinks|thirst|three/

     -> /th(at|i(?:(?:nk)?s|rst)|ree/   ?
     -> /th(?:at|is|inks|irst|ree)/     ?
     -> /th(?:at|i(?:nk)?s|irst|ree)/   ?