Hi Fred!

Fred Drake wrote:
On 11/10/06, yuppie <[EMAIL PROTECTED]> wrote:
While pointing the label to the div element that contains the input
fields is not very useful, this seems to be valid HTML::

Sorry for not replying earlier, but I wanted to have time to think
before responding.  ;)

No problem. Thanks for your feedback!

There's valid according to the DTD (the XML definition of validity),
and there's valid according to the specification.  DTDs aren't able to
specify the constraint documented in the specification document; in
this case, that means the DTD can be used to help detect invalid HTML
documents, but not determine whether an HTML document is valid.  More
expressive schema languages could be used to produce a more useful
schema definition.

Given that the specification clearly states that the "for" attribute's
value be an ID for a control, I must conclude that referring to the ID
of a <div> or other non-control element causes the HTML to be invalid.

I agree with your analysis, but I'm not sure I agree with your conclusions:

Looking at the output generated by formlib, I got the impression nobody cares much about valid output. I would be happy if formlib would return HTML that validates in a validator. Adding additional complexity for getting the label issue perfectly right doesn't fit much to the rest of the code. And I doubt any browser will have trouble with 'for' attributes pointing to a non-control element.

Making sure that radio and checkbox widgets have a div tag with the
required ID is a simple bugfix. No API changes are required and
zope.formlib still can use the widget name in the 'for' attribute.

Regardless of the HTML specification, this is a semantic change in the
contract of the IWidget API.  So it's a change, just not in the set of
attributes and methods and their signatures.

So IBrowserWidget's __call__ method *has to* return a snipped that
contains a tag with the widget's name as ID. All widgets that don't
follow that rule have to be fixed.

If there are no objections, I'll make the required changes on 3.2
branch, 3.3 branch and trunk.

I object; this is still a change to the contract.

Well. It depends on the point of view. This seems to be the implicit contract. The templates in zope.formlib and in zope.app.form use the widget name in the 'for' attribute, so they depend already on that behavior. Making this contract explicit by fixing the description in the interface doesn't mean to change the contract. Or does it?

You were on the right track with your first proposal.  There's a need
for widgets to provide more information to support integration in a
form.  Unfortunately, adding an attribute to the IWidget or other
existing interfaces doesn't work well, since it makes it harder to
write code that supports multiple versions of Zope.

So there is no way to fix interfaces? Are all interfaces completely frozen? (I still have to make myself familiar with the Zope 3 policies.)

Another way to expose the required information is to create a new
interface and provide adapters for the existing widgets (possibly by
simply implementing the new interface on the existing widgets).  A
form that's aware of the new interface can use the additional
information.

The new interface could look something like this:

   class IWidgetControlInformation(zope.interface.Interface):
       labelControlId = zope.schema.TextLine(
           title=_("Label control id"),
           description=_("Id of the control element that should be"
                         " associated with any <label> element rendered"
                         " for the widget."),
           required=False,
           )

       focusControlId = zope.schema.TextLine(
           title=_("Focus control id"),
           description=_("Id of the control element that should be"
                         " focused when the form is initially rendered."
                         " Since each widget may suggest an element for"
                         " the initial focus, this should only be regarded"
                         " as a hint."),
           required=False,
           )

This looks like overkill to me. No use case comes to my mind where focusControlId would be different to labelControlId.

But if Zope 3 policies require a new interface for changes like that and if we really want to stick that close to the HTML specification I'm fine with adding IWidgetControlInformation.


Cheers,

        Yuppie

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