Suggesting, not overwriting
The pill at the right of the top bar has two states. In Editing, what you type replaces what was there. In Suggesting, it arrives as a tracked change with your name on it, and the old text is still underneath.
This is the same mechanism that handles changes arriving from your other machine, which is why nothing ever overwrites your book behind your back. Every incoming edit is a suggestion until you accept it.
The margin
Select some words and press Comment — or ⌘⇧M. The comment anchors to the words it is about, so it moves when they move and it does not drift when the paragraph above it grows.
Comments take replies, can be resolved, and can be deleted. A resolved comment stops counting in the status bar but is not thrown away.
The six panels
The panel on the right is six things behind six tabs.
Changes lists every tracked edit, with accept and reject one at a time or all at once. Proof groups what the proofreader has found by kind, and lets you tell it to leave a particular passage alone. Outline is the book from above.
Proofing that stays on your machine
Underlines appear as you type, from a proofreader that runs locally. Nothing is sent anywhere to produce them — which, again, is why they work offline.
Your own rules live in Config: names, house spellings, the things you always want your way. They override everything else, and they are yours rather than a service’s.
Notes and research
The Notes tab holds sticky cards — coloured, movable, and attached to the book rather than to any one section. The Research tab holds clippings: paste, drag or upload, and Word documents, PDFs and images all land as cards you can open beside the manuscript.
Neither is part of the manuscript, so neither turns up in an export. That is the point of them.