OptionalchordThe chord sounding under the pitch, when the caller holds it.
A chord names its own tones better than its root alone can: it carries the
degree it writes each tone as, so a pitch that is one of its tones is
spelled exactly as spellChord spells it. Supersedes chordRoot,
which stays for callers holding nothing but a root pitch class.
OptionalchordRoot pitch class of the chord sounding under the pitch, when known.
OptionalpreviousThe pitch immediately before this one (MIDI pitch or bare pitch class).
OptionalnextThe pitch immediately after this one (MIDI pitch or bare pitch class).
The musical evidence around a pitch, used to refine an enharmonic choice the key alone cannot make.
Every field is optional and every field is only ever advisory: a context that says nothing about the pitch leaves its key spelling untouched.