Beam groups must reveal syncopation against the beat grid, never regroup to obscure it

Beam boundaries always mirror the underlying metric beat grid, even across syncopated rhythms; syncopation is shown through note spelling and ties, never by re-grouping the beam to visually smooth over an off-beat entrance. Keeping group boundaries fixed on the beat is precisely what makes an off-beat note's entrance visible — it starts mid-group or crosses into the next beat's ties rather than sitting at a group's left edge.

An eighth-tied-to-quarter-tied-to-eighth figure syncopated across beat 2 of a 4/4 bar has its surrounding beamable notes regrouped so a beam visually spans from beat 1 into beat 2 to 'show' the tie shape, instead of keeping normal per-beat groups with the tie drawn as a separate curve.

Gould, Behind Bars, ch. Beaming, cautions against using beam groups to disguise the meter; Read, Music Notation, similarly treats beat-grid-honest beaming as the default even under syncopation. Contrast: some modern jazz/commercial lead-sheet engraving (not documented by Gould, Read, Ross, or Stone as common-practice convention) deliberately beams BY RHYTHMIC FIGURE rather than strict beat, to visualize a swung/syncopated shape. Gradus's curriculum (Fux species counterpoint, chorale, fugue) is classical common-practice notation, so recommend Gradus enforce the strict beat-grid rule unconditionally, with no jazz-style opt-out.

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