New in version 2.0.
Yield topmost components in expr grouped by type:
abjad> staff = Staff(leaftools.make_leaves([0, 2, 4, None, None, 5, 7], [(1, 8)]))
abjad> for x in componenttools.yield_topmost_components_grouped_by_type(staff):
... x
...
(Note("c'8"), Note("d'8"), Note("e'8"))
(Rest('r8'), Rest('r8'))
(Note("f'8"), Note("g'8"))
Return generator.