New in version 1.1.
Count length-2 runs in sequence:
abjad> from abjad.tools import sequencetools
abjad> sequencetools.count_length_two_runs_in_sequence([0, 0, 1, 1, 1, 2, 3, 4, 5])
3
Return nonnegative integer.
Changed in version 2.0: renamed sequencetools.count_repetitions() to sequencetools.count_length_two_runs_in_sequence().