Bases: abjad.core.abjadcore._Abjad
Spacing indication token.
LilyPond Score.proportionalNotationDuration will equal proportional_notation_duration when tempo equals tempo_indication.
abjad> tempo = TempoIndication(Rational(1, 8), 44)
abjad> spacing_indication = SpacingIndication(tempo, Rational(1, 68))
abjad> spacing_indication
<SpacingIndication>