A tuplet spanning more than one primary beat (e.g. a hemiola or duplet) is legitimate and must not be flagged as an error — only surfaced for author confirmation

Unlike ties and dots, tuplets are not restricted to starting and ending within a single primary beat: a hemiola (e.g. 2 dotted quarters in the space of 3 in 6/8, spanning the whole bar) or an across-the-beat duplet is standard, intentional notation, not a fault. The bracket itself makes the grouping visually explicit, so beat-crossing does not obscure the pulse the way an unbracketed tie-vs-dot violation would.

N/A as a hard violation — the concern named in this domain's brief ('tuplets that cross a beat') is a request for visibility/confirmation, not a defect, since beat-crossing tuplets are a legitimate and common shape (hemiolas especially). Flagging this as an error would misstate a universal where practice deliberately varies (review criterion #3/#4).

Gould, Behind Bars, ch. 'Tuplets', hemiola and cross-beat tuplet examples treated as ordinary notation, not a special case requiring justification.

This rule can be decided from pitches, durations and voices — no layout required. A validator can check it before anything is drawn.