when I tried to find out the name of the command that moved the border
of the upper window (i.e., the lower border of that window) with the
upper arrow key, `C-h k' (describe-key) failed and I continued to move
the border.
I was not able to exit Emacs with `C-x C-c'
(save-buffers-kill-terminal) either, not until I quit editing the
windows with `q'. Then I was able to quit.
Certainly, `window-edit' should not disable `C-h k' (describe-key) or
`C-x C-c' (save-buffers-kill-terminal).
The other library, winsize.el, also does not let you discover what an
arrow key does when C-x + is active.