Re: mouse-drag-mode-line should maybe use window-tree

[Richard M. Stallman]

    Sorry, forgot to write that it is the code in `mouse-drag-window-above' 
    that looks suspicious to me. It seems like it only compares the top of 
    the parameter window with the bottom of other windows.

Yes, it is finding a window whose bottom is at the same height
as the top of this one.

Are you saying it might find the wrong window?  It could find a window
that ends at the same vertical position as the right window, but is
located to the side of it?

I am not sure if that bug can occur.  Can you add code to
verify that the window found overlaps in the horizontal dimension
with the given window?