Model A cannot author an acciaccatura (slashed grace note) — only appoggiatura-style

A slashed grace note (acciaccatura) is played as fast as possible before the beat and takes no perceptible time from the main note; an unslashed grace note (appoggiatura) takes a defined, often substantial, rhythmic value from the main note. The two look different (slash through the stem) and are notationally distinct, not just performance nuance.

Gould, Behind Bars, ch. Grace Notes — explicit slashed/unslashed distinction; Read, Music Notation, and standard Baroque performance practice treat these as different notated objects, directly relevant to Gradus's Bach curriculum.

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