Model A cannot author combination articulations (e.g. portato)

Portato (a sustained-but-separated touch) is notated as a staccato dot AND a tenuto line together on one notehead — a legitimate, named combination, distinct from either mark alone.

Gould, Behind Bars, ch. Articulation — lists staccato+tenuto (portato) as the one standard combination mark in common use; Read, Music Notation, gives the same combination under "mezzo staccato"/portato.

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