Measures in ‘measures’ may be strictly parent-contiguous.
Or measures in ‘measures’ may all be outside-of-score.
Measure fusion across intervening container boundaries is undefined.
Calculate best new time signature and instantiate new measure.
Give contents of ‘measures’ to new measure.
Give dominant spanners of ‘measures’ to new measure.
If parentage of in-score ‘measures’ to new measure.
‘Measures’ end up empty, undominated and outside-of-score.