A down-stem voice's beam sits BELOW its noteheads even when those noteheads are high on the staff — the direct visual consequence of the stem-role fixation

Beams attach at the stem tip, so a voice locked to down-stems draws its beam below the notehead row for that group, regardless of how high those notes actually sit on the staff. A reader must not interpret 'beam below' as 'these are low notes' on a shared stave — it means 'this is the down-stem voice,' which can be sounding above the up-stem voice at that moment (see voice-crossing-definition-and-tolerance).

A down-stem voice's beam drawn above its noteheads (or vice versa) because `maintain_stem_directions` was dropped from a `Beam.generateBeams` call and the beamer recomputed stem/beam side from pitch instead of the forced role — see beam-renderer-contract for the exact code guard.

Gould, Behind Bars, and Ross, The Art of Music Engraving — beam side is a direct function of stem side, which is itself fixed by voice role on a shared stave; this is not a separate convention but the observable consequence of voice-numbering-role-fixation, worth stating on its own because it is the concrete visual symptom Sean specifically called out.

This rule is about where marks land on the page, so it can only be judged after engraving. Collision and spacing faults live here.