Checkbox Three States

[Etienne]

Hello,
I'm searching a webcontrol Checkbox Three States. I saw many times on the
web that it's not possible. I don't why ! I think it is with javascript and
asp.net.
Have you got a source please ?
Thank you.

 

[Etienne]

Finally, I have made the component with three checkbox images : javascript
when click and retrieve image name from client when update.