New in version 2.3.
True when expr is a component with key signature mark attached:
abjad> staff = Staff("c'8 d'8 e'8 f'8")
abjad> contexttools.KeySignatureMark('c', 'major')(staff)
KeySignatureMark(NamedChromaticPitchClass('c'), Mode('major'))(Staff{4})
abjad> f(staff)
\new Staff {
\key c \major
c'8
d'8
e'8
f'8
}
abjad> contexttools.is_component_with_key_signature_mark_attached(staff)
True
Otherwise false:
abjad> contexttools.is_component_with_key_signature_mark_attached(staff[0])
False
Return boolean.