AS NEEDED split screen for editing

I would really love to have the ability to split the screen when necessary and look at two version of my text: the original and the changes I'm trying to make. This is helpful for comparing/contrasting. Sometimes I only need to edit a few words here and there for stronger word choice or passive voice. But other times , whole sections need to be completely rewritten and I want to be sure I'm keeping my original intent in my changed text. (Perhaps this could be part of an overall large-scale "Editing Mode" that also includes the ability to track changes and keep multiple drafts of the same book?)