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

[Richard M. Stallman]

    After spending some time wondering why you wrote the new function I 
    realized that it was just enough to nicely fit the needs of the resizing 
    functions. The new function also seems to work in all cases I have 
    tested so far.

If you're not careful about the order in which you move the edges,
adjust-window-trailing-edge can easily give you an error.  The reason
is that it never moves any edges above or below the one you specify to
move, and it can't make any window too small.

If you're not careful about the order to move the edges,
some intermediate state could easily be invalid, resulting
in an error.

Perhaps your code copes with this issue already.  If not, it needs to.