Lyric syllabic position is not represented (model gap)

Every lyric syllable in MusicXML/engraving carries a syllabic role — single (whole word on one note), begin, middle, or end (a word split across notes) — which determines whether a hyphen is drawn after it. This is the load-bearing datum for every hyphenation, melisma, and system-break rule below; without it none of them are computable.

MusicXML 4.0 lyric/syllabic enumeration (single|begin|middle|end); Gould 'Word underlay'; Ross ch.20.

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