@rule('<STR_LIT>')<EOL><INDENT>def visit_next_unnamed_arg(self, _, children):<DEDENT>
return children[<NUM_LIT:1>]<EOL>
Unnamed argument of a filter following a previous one (so, preceded by a comma).

        Arguments
        ---------
        _ (node) : parsimonious.nodes.Node.
        children : list
            - 0: for ``COM`` (comma): ``None``.
            - 1: for ``UNNAMED_ARG``: instance of ``.resources.PosArg``.

        Returns
        -------
        .resources.PosArg
            Instance of ``.resources.PosArg``.

        Example
        -------

        >>> UnnamedArgsParserMixin(r', 1', default_rule='NEXT_UNNAMED_ARG').data
        1
        >>> UnnamedArgsParserMixin(r',"foo"', default_rule='NEXT_UNNAMED_ARG').data
        "foo"
        >>> UnnamedArgsParserMixin(r', null', default_rule='NEXT_UNNAMED_ARG').data
        None
        >>> UnnamedArgsParserMixin(r', FALSE', default_rule='NEXT_UNNAMED_ARG').data
        False
        >>> UnnamedArgsParserMixin(r', True', default_rule='NEXT_UNNAMED_ARG').data
        True