Algunes regles poden tenir regles fill que s' executen únicament si la regla pare resulta aplicable. A tota la cadena coincident se us donarà l' atribut definit per la regla pare. Una regla amb regles fills te aquest aspecte:
Some rules can have child rules which are then evaluated only if the parent rule matched. The entire matched string will be given the attribute defined by the parent rule. A rule with child rules looks like this: