Parse nested rulesets
            and save it in cache.

def parse(self, target):
        """ Parse nested rulesets
            and save it in cache.
        """
        if isinstance(target, ContentNode):
            if target.name:
                self.parent = target
                self.name.parse(self)
                self.name += target.name
            target.ruleset.append(self)
        self.root.cache['rset'][str(self.name).split()[0]].add(self)
        super(Ruleset, self).parse(target)