Parse and/or compile given rule into rule tree.

        :param rule: Filtering grammar rule.
        :return: Parsed and/or compiled rule.

def prepare(self, rule):
        """
        Parse and/or compile given rule into rule tree.

        :param rule: Filtering grammar rule.
        :return: Parsed and/or compiled rule.
        """
        if self.parser:
            rule = self.parser.parse(rule)
        if self.compiler:
            rule = self.compiler.compile(rule)
        return rule