javascript API help

It's all a bit overwhelming! I"m trying to do something pretty simple... I want to mark adds and deletes in the editing window like MSWord "track changes". So instead of delete, the text to be deleted will be rendered with line through in red, and when adding text, the added text is rendered in red.

Can someone who is familiar with the js API suggest which "hooks" to use to implement this? I'm not looking for a complete solution... just some pointers.

Thanks in advance

Les