Three stage checkbox?

[FlexibleLearning at aol.com]

On a PC the default 'mixed' state is a tick in a grey-shaded checkbox .

On a Mac, the default 'mixed' state is a dash '-' a white checkbox (maybe OSX 
is different).

If native rev support for this were to be provided, as I think it should, it 
would make more sense to conform to the existing interface standards than 
invent a new one.

The easiest way to show all checkbox states would be to activate one of two 
three-frame gifs, one if the platform is MacOS and the other if the platform is 
win32.

My 2c.

> I like the idea of a checkbox with a question mark inside it.
> An interesting (and clear to me) interface element.

/H