New in version 2.0.
Get stem tremolo attached to component:
abjad> staff = Staff("c'8 d'8 e'8 f'8")
abjad> marktools.StemTremolo(16)(staff[0])
StemTremolo(16)(c'8)
abjad> f(staff)
\new Staff {
c'8 :16
d'8
e'8
f'8
}
abjad> marktools.get_stem_tremolo_attached_to_component(staff[0])
StemTremolo(16)(c'8)
Raise missing mark error when no stem tremolo attaches to component.
Raise extra mark error when more than one stem tremolo attaches to component.
Return stem tremolo.