[GUI] Setting properties of a widget.

[Vincenzo Ciancia]

On Tue, 1 Apr 2003 09:56:10 +0100
Axel Simon <A.Simon@ukc.ac.uk> wrote:

> Callbacks would
> otherwise be the only "attributes" which return something when they
> are set.

Yes, that's a good point. As an alternative, you can have things that
can have a callback installed, things that can be read, written etc. 

Since the already mentioned filters for variables are like callbacks,
this means that a variable "can have a callback" and "can be read" and
"can be written", while the mouse position "can have a callback" and
nothing else (just an example, in the particular case of the mouse
position, if there is a separate function for getting the position at a
particular moment without installing a callback, then the mouse position
"can be read" also, but can't be written indeed).

Vincenzo