Apply positioning to expr. Music expr must already be marked with line breaks.
abjad> t = Staff(RigidMeasure((2, 8), construct.run(2)) * 4)
abjad> pitchtools.diatonicize(t)
abjad> layout.line_break_every_prolated(t, Rational(4, 8))
\new Staff {
\time 2/8
c'8
d'8
\time 2/8
e'8
f'8
\break
\time 2/8
g'8
a'8
\time 2/8
b'8
c''8
\break
}
abjad> systems = SystemYOffsets(40, 5)
abjad> staves = StaffAlignmentOffsets(0, 15)
abjad> positioning = FixedStaffPositioning(systems, staves)
abjad> layout.apply_fixed_staff_positioning(t, positioning)