Notification for a changed boundary between ranges. For example,
if the same span is covered by two partial ranges before and one
bigger range after, this is called at the point where the ranges
used to be split.
Notifies the comparator that a range (in positions in the new
document) has the given sets of values associated with it, which
are different in the old (A) and new (B) sets.
Collection of methods used when comparing range sets.