Case encodes chord quality: uppercase for major/augmented, lowercase for minor/diminished, with degree and augmented symbols

A roman numeral is written in uppercase for a major or augmented triad, lowercase for a minor or diminished triad, with a small superscript diminished-circle symbol appended for a diminished chord and a plus for augmented. This is the near-universal convention across harmony pedagogy that Dorico's Roman Numeral Analysis feature also implements.

A minor chord is labeled with uppercase when the chord's actual pitch content is minor, or a diminished chord is labeled without the diminished symbol.

Aldwell and Schachter, Harmony and Voice Leading (standard convention); Dorico Roman Numeral Analysis behavior mirrors this exactly.

Gould/Read/Ross do not cover analytical roman numerals in depth since they are a harmony-pedagogy convention rather than a strict engraving-tradition one — Gradus should follow the harmony-pedagogy authorities here, an explicit noted authority gap relative to the other rules in this chapter.

Our own judgement, not a sourced convention — shown separately so the two are never confused.

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