The 'Z0' movetext extension is not accepted.

[RogerMarsh]

'Z0' is used as a null-move marker by some PGN file sources. This appears to be an alternative to '--' used for the same purpose by other PGN file sources and already accepted as a valid token.

'--' is treated as an error, because the movetext does not describe a game, and 'Z0' will be treated as an error too.

Currently 'Z0' is treated as the illegal token 'Z' followed by text starting with the move number character '0'.