Would it be possible to have an option to lower a window to the bottom of the stack? So that it was obscured by other windows that overlap it?
Back in the days I used X-windows on unix most window managers provided this functionality and it was incredibly useful.
For example, if I have some windows on the screen I am working with and they are all obscuring some large window like Thunderbird or something, I can raise Thunderbird with the Alt-Tab sequence. But then I have to raise each of the other windows I was using individually. There is no way to lower Thunderbird back to the bottom. Being able to Cmd-Click (or whichever trigger) the window to send it back to the back would be very useful.