Strong Undo/Redo

[Ofnuts]

Yes, they are. From the source code:

For undo:

Code:

/*
 * this function continues to undo as long as it only sees certain
 * undo types, in particular visibility changes.
 */

For redo:

Code:

/*
 * this function continues to redo as long as it only sees certain
 * undo types, in particular visibility changes.  Note that the
 * order of events is set up to make it exactly reverse
 * gimp_image_strong_undo().
 */

So it is mostly about skipping visibility changes in the undo stack.