Undo

[ElDragonRojo]

Here is where being backed by GitHub really makes sense.

When there are changes, instead of going back to being a back button, the cancel button should be the undo button.

[ElDragonRojo]

The undo button should be a permanent fixture, and it should let you undo forever, by rolling back commits, leveraging the power of GitHub.

[ElDragonRojo]

There should be another mode (perhaps by long-pressing undo) that puts the document two-up and shows a diff with the current version.

You should then be able to save a copies thereby creating a branch.