Using <backup> it is possible to have ‘incomplete’ measure lengths. This test starts with a quarter note upbeat and a whole note for voice 1 in the first measure, and voice 2 contains only a quarter note starting at the second beat. The second measure contains whole notes for both voices. Note that there is a discontinuity in the MusicXML timing: voice 2 ‘jumps’ from the single quarter note to the whole note in the second measure. 1 C 5 1 1 quarter C 5 4 1 whole 3 C 4 1 2 quarter C 5 4 1 whole 4 C 4 4 2 whole