This is a silly little question that neither the Help stuff
nor google seems to answer ...
On other unixoid systems with X-windows, a very handy technique
for finding a window that's buried somewhere in that jjumbled
pile of windows is to "background" windows until the one you're
looking for appears. With most window managers, this is done
with a middle-button click on the border, though sometimes it
is other things like CTL-middle.
I haven't found any way to do this on OSX. You can move and/or
close windows until you uncover the one you want, but this isn't