Optionalflats?: booleanWhich side of the staff the whole symbol is written on: true writes it in
flats, false in sharps. The root, the slash bass and the chord's tones are
spelled together, so a symbol never pairs a flat root with a sharp bass, and
a spelling hint already on the requested side is kept rather than renamed.
Where that side cannot spell the chord at all, the spelling a chart writes
wins over an unwritable one.
How a chord symbol is written: in which notation system, and on which side of the enharmonic fence.