Problem there is that the widget then has no border at all and it is my opinion that this looks crap That's why I implemented the dual valid/invalid class switch so at least there is always a 1px border.
Maybe I'll re-visit this some other time.
but it does have a border! Or at least it should.
When creating this.el, afterwards add this to make it a normal field:
It will then be x-form-field, and it will have a border!