Example of button attribute of Shape element.

Can anyone provide an example of a .vml Shape element with a button
attribute that shows how to reference the button state?

This is probably an elementary question for experienced xml / vml
developers, but I'm really stuck.  The only documentation I can find on
this is in the MSDN Library Reference for VML which does not show how to
reference the button state.

Any help would be appreciated.

Thanks, Tom