[BlueTemplar]

The browser is the wrong platform for anything that isn't an HTML document, and not only for performance reasons, but perhaps much more importantly : for interface reasons.

For instance : in your typical windowed program, when you press "Alt", it's supposed to show the Menu, which you can then quickly navigate using keyboard shortcuts. You can't do that properly inside the browser because it's going to conflict with the browser's own Alt-Menu.

[tshaddox]

Based on inspecting the DOM of the read-only preview document they link to, my guess is that they will be using traditional DOM elements for much of the editing UI. There appear to be many empty DOM elements that are there to hold various toolbars and other UI elements. And for what it's worth, there seem to be empty DOM elements intended to be read by screen readers.