Returns true if the given key should use flat accidentals for note naming.
Uses circle-of-fifths logic extended to the church modes and the modes of harmonic and
melodic minor. For major-family modes, the parent Ionian key is looked up in the circle;
for minor-family modes, the parent minor key (a minor tonic is looked up by its own name).
Falls back to checking the root's own accidental for unknown scale types.
Parameters
rootName: string
Root note name (e.g. 'D', 'Bb', 'F#'). Octave digits are stripped.
scaleType: string = 'major'
Scale or mode type (e.g. 'major', 'dorian', 'harmonic minor'). Default: 'major'.
Returns true if the given key should use flat accidentals for note naming.
Uses circle-of-fifths logic extended to the church modes and the modes of harmonic and melodic minor. For major-family modes, the parent Ionian key is looked up in the circle; for minor-family modes, the parent minor key (a minor tonic is looked up by its own name). Falls back to checking the root's own accidental for unknown scale types.