Voice overlap (a voice moving beyond an adjacent voice's PREVIOUS position) is a voice-leading concept, not a shared-stave engraving hazard

Voice overlap occurs when a voice moves to a pitch beyond where an ADJACENT voice was on the immediately preceding onset (not simultaneous with it) — e.g. Alto's new note is higher than Soprano's prior note, even though Alto and Soprano don't cross at any single instant. This differs from crossing (a within-simultaneity phenomenon) and has no direct rendering consequence on a shared stave — it doesn't itself cause a notehead, stem, or beam collision.

N/A for engraving — overlap is a composition-pedagogy concern (belongs to a voice-leading/counterpoint chapter, not this one), included here only so the two terms are not confused going forward.

Standard voice-leading/part-writing terminology (Fux-derived species-counterpoint pedagogy, which Gradus already teaches); included here for definitional completeness because a prior draft's naming conflated 'crossing' and 'overlap' under one heuristic.

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