Am Donnerstag 28 August 2008 10:14:11 schrieb Martin Aspeli:
> Marius Gedminas wrote:
> > On Wed, Aug 27, 2008 at 05:15:48PM -0700, Stephan Richter wrote:
> >> On Wednesday 27 August 2008, Martin Aspeli wrote:
> >>> 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?
> >>
> >> I think you have a point. Have you tried changing the behavior to
> >> return "default" and see what tests fail? If no major failures come out
> >> of this, I would say change it.
> >
> > Wait a second, maybe I'm misunderstanding this, but I certainly oppose
> > any change that would make an unchecked checkbox an error during form
> > validation.
> >
> > A required Bool field can have two values: True or False.  One is
> > represented by a checked checkbox, the other by an unchecked checkbox.
> > An unchecked checkbox is not missing input and should not trigger
> > "required missing" errors.
> What about the case when you have a list of options of which you need to
> chose one or more? In that case, ticking none is a validation error.

Yes, in your case this should give a validation error. However, the case where 
someone uses a checkbox for a True/False operation is at least as common. And 
if "no ticking" gives a validation error, this would prevent using checkboxes 
for this case. Moreover, a checkbox is typically used to represent a "Bool" 
schema (by default it's a choice widget, I think), so that fits well, I 

My suggestion would be to:

- Create some schema field, e.g. "MultipleChoice":

colors = MutlipleChoice(title='Colors', values=['red', 'green', 'blue'], 
default=['green', 'blue'], required=True)

- Register a widget for this field, which is then rendered as a bunch of 

Best Regards,

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