I can't find what I'm looking for: api/tinymce/tinymce.undomanager.html

I've tried to understand how to use the undo manager when authoring a TinyMCE plugin. I don't understand the overall philosophy:

• What is an Undo Level (add) vs.
• What is an Undo Bookmark (beforeChange)
• What is the best practice for using the api if I am supplying the user a button that styles content, mutates the document?
• Do I need to always use transact to call my mutator function? Or is it a option? What's the best practice?

For example, my plugin provides an interface for selecting text and wrapping it with a so they can markup the human language changes in the text. It does that by applying a format. I've tried every combo I can imagine to make it work with undo to no avail.

Start with api/tinymce/tinymce.undomanager.html and review how it defines Undo Levels, Undo Bookmarks, and transact. Clarify the recommended workflow for a plugin that applies a format to selected text, including when each API should be used and what the resulting undo behavior should be.