Package-level declarations

A Batch is part of a History and is made up of a list of Changes. Undo and redo work on batches, not on individual changes.

See History and Batch.

All concrete implementations of Change must also implement this. However, the public API must never expose this implementation, because undo and redo must only be called by History.

The mechanism underlying undo and redo. It is called History, because I think of undo as going back in time, and redo as going forward in time.

A document with a History, allowing undo and redo actions.

Changes which do not change the model's data are skippable. e.g. changes to the current selection are SkippableChanges.

Using weak listeners can help prevent memory leaks.