Raised by: Glen in mail.
Discussion: Glen: "For type checkbox, the input should be set to a checkedness of true." It would be nice to have a way to allow user to say something to set it to false, but I can't think of a good convention for this other than adding an attribute or grammar. Perhaps this could/should only be possible via scripting. (I don't like the idea of toggling the checkbox because some users may not be able to easily observe what state the checkbox is currently in.) Michael: When using the default grammar and default binding we could have some sort of "unset" prefix grammar and if you match that uncheck the element, but in general I think this is an example of complexity best handled by scripting (unless someone can think of something simple and brilliant).
Resolution: See issue 11