bug#14964: 24.3.50; doc of `compare-window-configurations'

[martin rudalics]

> E.g. (current-frame-configuration t) would return a writable & readable
> frame configuration.

With configurations you store and restore window positions and sizes in
situ.  That is, you overwrite (in C) the members of the window structure
and rely on the fact that a configuration is an immutable memory object
to obtain correct bahavior.  A function like `set-window-configuration'
does not check whether the object it restores is correct in some sense
or has been manipulated after it has been stored.  It relies on your
hardware to do that.  `window-state-put' OTOH is pretty failsafe in this
regard because it restores windows via the Lisp split and resize
operations.

> But the point is to have a standard structure that code can use and
> manipulate.

That would be clearly fatal as explained above.  Changing anything in a
frame configuration is strictly forbidden.

martin