Chord-symbol quality and extensions use the closed standard abbreviation set

Chord-symbol quality/extension text uses the closed standard set: maj7 (or a triangle glyph), m7 or -7 (minor seventh), m7b5 (or a half-diminished circle-with-slash glyph), dim7 (or a diminished-circle glyph), aug or + (augmented), sus4/sus2, and altered/added extensions written as 7#9, 7b13, 9, 11, 13, etc. Slash-bass inversions are written as a single root/bass unit (e.g. C/E), never as two stacked symbols. Spelled-out words ('Major seven', 'flat five') and an ambiguous bare lowercase 'm' meant to signal major are nonstandard.

A chord symbol string is authored as 'Cmaj' (ambiguous against a minor 'm'), or 'Csus' without specifying 4 or 2, or a slash-bass chord is written as two separate stacked symbol objects rather than one root/bass unit.

De facto jazz-real-book/Berklee convention, also the basis of SMuFL's chordSymbol glyph range; Dorico/Finale chord-symbol input systems enforce the identical closed set.

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