@rule('<STR_LIT>')<EOL><INDENT>def visit_filter_args(self, _, children):<DEDENT>
return children[<NUM_LIT:0>] if children else None<EOL>
The optional arguments of a filter.

        Arguments
        ---------
        _ (node) : parsimonious.nodes.Node.
        children : list
            - 0: list of instances of ``.resources.NamedArg`` or subclasses,  or None

        Returns
        -------
        list(.resources.NamedArg)
            List of  instances of ``.resources.NamedArg`` or subclasses, or ``None`` if no
            parenthesis.

        Example
        -------

        >>> FiltersParserMixin(r'', default_rule='FILTER_ARGS').data

        >>> FiltersParserMixin(r'()', default_rule='FILTER_ARGS').data
        []
        >>> FiltersParserMixin(r'(1)', default_rule='FILTER_ARGS').data
        [1]
        >>> FiltersParserMixin(r'(1, bar="baz")', default_rule='FILTER_ARGS').data
        [1, bar="baz"]