Hi, In z3c.form.widget.SequenceWidget, we have: def extract(self, default=interfaces.NOVALUE): """See z3c.form.interfaces.IWidget.""" if (self.name not in self.request and self.name+'-empty-marker' in self.request): return [] value = self.request.get(self.name, default) if value != default: for token in value: if token == self.noValueToken: continue try: self.terms.getTermByToken(token) except LookupError: return default return value This means that if the request contains the empty-marker only (no selection was made) for a checkbox widget (say), then the return value is [], rather than default (NOVALUE). Is that a bug? I have a custom checkbox widget derived from the standard checkbox widget, (z3c.formwidget.query, in fact), and I never get any "required missing" exceptions, even when I untick all the checkboxes and click OK. Am I missing something? Cheers, Martin -- Author of `Professional Plone Development`, a book for developers who want to work with Plone. See http://martinaspeli.net/plone-book