The specifiers M % +M can only occur in seventh chords and therefore one of 7 65 43 2 needs to follow it. Since form and figbass are defined in two separate groups, the regex matches even if figbass is missing. To improve the regex would probably require lookaheads. Or we check that elsewhere and/or do some automatic correction, just assuming 7?
The specifiers
M % +Mcan only occur in seventh chords and therefore one of7 65 43 2needs to follow it. Sinceformandfigbassare defined in two separate groups, the regex matches even iffigbassis missing. To improve the regex would probably require lookaheads. Or we check that elsewhere and/or do some automatic correction, just assuming7?