Matches a display text value

def _match_display_text(self, element_key, string, string_match_type, match):
        """Matches a display text value"""
        if string is None or string_match_type is None:
            raise NullArgument()
        match_value = self._get_string_match_value(string, string_match_type)
        self._add_match(element_key + '.text', match_value, match)