Yield the left-to-right, top-level contents of expr with chain-wrapped leaves.
t = Staff(construct.notes(0, [(5, 32)] * 4))
t.insert(4, FixedDurationTuplet((2, 8), construct.run(3)))
pitchtools.diatonicize(t)
abjad> print t.format
\new Staff {
c'8 ~
c'32
\times 2/3 {
d'8
e'8
f'8
}
g'8 ~
g'32
a'8 ~
a'32
b'8 ~
b'32
}
abjad> for x in iterate.chained_contents(t):
... x
...
(Note(c', 8), Note(c', 32))
(Note(d', 8), Note(d', 32))
FixedDurationTuplet(1/4, [e'8, f'8, g'8])
(Note(a', 8), Note(a', 32))
(Note(b', 8), Note(b', 32))
Crossing ties raise TieChainError.