@classmethod<EOL><INDENT>def check_extension(cls, ext):<DEDENT>
if ext.startswith('<STR_LIT:.>'):<EOL><INDENT>ext = ext[<NUM_LIT:1>:]<EOL><DEDENT>if not any(ext in extension for extension in cls.supported_extensions):<EOL><INDENT>msg = ("<STR_LIT>"<EOL>.format(engine=pprint_thing(cls.engine),<EOL>ext=pprint_thing(ext)))<EOL>raise ValueError(msg)<EOL><DEDENT>else:<EOL><INDENT>return True<EOL><DEDENT>
checks that path's extension against the Writer's supported
        extensions.  If it isn't supported, raises UnsupportedFiletypeError.