Hook to enable/disable dijit.form.Button

[Marcel Overdijk]

On http://docs.dojocampus.org/dijit/form it's mentioned that:

Using the dijit.form.Form widget you can prevent form submission if any of the fields are invalid. Dijit provides hooks so you can either disable the submit button, or popup an error message when the user tries to submit, or even focus on the invalid field.

I like to disable my submit button as long as the form inputs are not valid. Where can I find more information how to use this hook? An example would be helpful.