Split chord into a disjunt (treble, bass) pair of parts about pitch. Place pitches in chord greater than or equal to pitch.attr into the treble part of the return pair. Place pitches less than pitch.attr into the bass part of the return pair.
In the usual case, chord is an Abjad Chord. But input may also be an Abjad Note or Rest.
Length treatment:
Note that both treble and bass return parts carry unique IDs. That is:
id(chord) != id(treble) != (bass)
Note also that this function returns only unspanned output.
Example:
abjad> chord = Chord(range(12), Rational(1, 4))
abjad> chord
Chord(c' cs' d' ef' e' f' fs' g' af' a' bf' b', 4)
abjad> chordtools.split(chord, Pitch(6))
(Chord(fs' g' af' a' bf' b', 4), Chord(c' cs' d' ef' e' f', 4))