Hi, At the moment, three form elements are barred from constraint validation: object, fieldset and output. I can understand why object and fieldset are barred from constraint validation but I think output could use the constraint validation.
Indeed, it could be nice to be able to use setCustomValidity() on <output>. IMHO, it is part of the use case of <output>: this element should represent the result of a calculation and we may want to do a validation check on this result. For example, we could imagine a web application to choose courses in an university and you have to select between 12 and 18 credits. <output> is the best way to represent the total credits used and it would be easy to make it invalid when the sum is not correct. Feedback is welcome :) Thanks, -- Mounir