XXX: YYY
   | 'something' 'else'
   | 'a' <reject>
   | 'this string' <reject>
   | ZZZ <reject>

YYY: 'some string'
ZZZ: 'ww' | 'xx' | 'yy' | 'zz'

##</code><code>##

$parser->start ($string);