+PROPS-C is an alist of properties to put (via overlays) on the changes.
+PROPS-R is an alist of properties to put on removed characters.
+PROPS-A is an alist of properties to put on added characters.
+If PROPS-R and PROPS-A are nil, put PROPS-C on all changes.
+If PROPS-C is nil, but PROPS-R and PROPS-A are non-nil,
+put PROPS-A on added characters, PROPS-R on removed characters.
+If PROPS-C, PROPS-R and PROPS-A are non-nil, put PROPS-C on changed characters,
+PROPS-A on added characters, and PROPS-R on removed characters.
+