M level number

m_level_number holds the next level number to go to after the current level is completed (via a nuke button, lotag 65534 or 65535 sectors, et cetera…). If you are going to use the startlevel command instead of hard-coded level switching behavior, using this is useful, although you could also simply add 1 to a copy of LEVEL.

See LEVEL, VOLUME, level_number, volume_number, and m_volume_number.