Check expr for well-formedness.
If expr is not well-formed, report violators and raise WellFormednessError.
abjad> t = Staff(construct.scale(4))
abjad> Beam(t[:])
abjad> t._music.pop( )
abjad> check.assert_wf(t)
0 / 1 beams overlapping
0 / 1 containers empty
0 / 3 flags misrepresented
0 / 0 glissandi overlapping
0 / 0 hairpins intermarked
0 / 0 hairpins short
0 / 4 ids duplicated
0 / 0 measures improperly filled
0 / 0 measures misdurated
0 / 0 measures nested
0 / 0 octavations overlapping
0 / 4 parents missing
0 / 3 quarters beamed
1 / 1 spanners discontiguous
0 / 3 ties mispitched
WellFormednessError
If expr is well-formed, return None.
abjad> t = Staff(construct.scale(4))
abjad> Beam(t[:])
abjad> t.pop( )
abjad> check.assert_wf(t)