Called when this window starts or stops editing together; swatches: whether its swatch library
is shared with the others too. The tabs are locked here rather than
through EditorUI.disable(): that takes pointer events away, and with them the tooltip that says
why. A locked tab keeps its name, adds the reason to its tooltip, and swallows the click that
would open it. The content bar's tabs are not keyboard-reachable yet (no role, no tabindex, for
every tab, not only these), so there is no key to swallow; aria-disabled is set for when they
are, and says nothing to a screen reader until then.
What stays out of reach while people edit one template together (TYP-919).
Editing together shares elements, pages and, where both sides can, the swatch library (
SwatchSync), not the document's styles or its fonts. A font or style added in one window would be one the others do not have: text using it lays out without it there, and the window that saves for everyone could save the template without it. So, until those are shared too, nothing that changes them is offered while the document is shared: replacing colours and fonts (POD settings), and the Templates and Clips tabs, whose pages and clips bring their own swatches, styles and fonts. Adding, editing and removing swatches stays out of reach too when the swatch library is not shared (a canvas withoutapply_remote_swatches()).