Yesterday, I discussed the way the Ribbon scales to different window sizes.  I've also mentioned that you can collapse the Ribbon by double-clicking the selected tab or by pressing Ctrl+F1.  One piece of the design I haven't yet written about but you might have noticed if you watched yesterday's movie is what happens to Office windows below about 250 pixels wide.

It's an idea we kind of stole from OneNote: when you size the window below a certain threshold, the whole Ribbon disappears, leaving you with just your document.  If you've used OneNote, you know that once you resize down below a certain threshold, most of the frame and commands disappear, leaving you with a clean little box to take notes in.  We've taken the idea now and expanded it to all new UI apps.

The logic goes like this.  Below a certain minimum size, no amount of downward scaling makes the UI truly usable.  (This is the case for previous versions of Office as well.)  So, a good assumption seems to be that you're not actually trying to use the commands anymore at that size, but instead you want the content of the document in a skinny window.  Maybe you want to have it up alongside another document that you're editing.  Maybe you're doing copy and paste from one document to another.  Or drag and drop.  But it's unlikely that you're trying to insert a caption or debug formulas in a window that narrow.

When you size the window back over the threshold, the Ribbon reappears, ready to follow your orders.

If you want to see what it looks like in action, check out the movie I posted yesterday (1.6 MB, Windows Media Format).

It's a small touch, but I think it adds a bit of polish to a scenario in which the UI has the potential to put its worst foot forward.