def __contains__(self, item):
if isinstance(item, str):<EOL><INDENT>return any([item == arg.value for arg in self])<EOL><DEDENT>return super().__contains__(item)<EOL>
Checks for membership. Allows string comparisons to args.

        >>> arguments = TexArgs(['{arg0}', '[arg1]'])
        >>> 'arg0' in arguments
        True
        >>> OArg('arg0') in arguments
        False
        >>> RArg('arg0') in arguments
        True
        >>> 'arg3' in arguments
        False