Creating functions for Undo and Redo?

Thinking out aloud.
Couldn't you create a function wrapping SetTextAreaText?
Create an object containing a field which holds the text added and have a variable point to the link for that object..
When you undo use prevlink and redo nextlink until you're at the top/bottom of the chain.
Each time you undo/redo remove/add the text from the object at that link.