[whatwg] Why children of datalist elements are barred from constraint validation?

[Ian Hickson]

On Fri, 31 Dec 2010, Mounir Lamouri wrote:
> On 12/31/2010 03:20 AM, Ian Hickson wrote:
> > On Fri, 24 Sep 2010, Mounir Lamouri wrote:
> >>
> >> I agree that a child of a datalist element should not block the form 
> >> submission. However, I'm wondering why do we care about this 
> >> particular edge case when there are a lot of situations where an 
> >> element can be invalid without any possible action from the user.
> >>
> >> If there is no specific use cases in mind I think we should just 
> >> remove that.
> > 
> > It's so that you can use a <select> in the <datalist> (with the same 
> > <option>s) for fallback in older UAs, without that <select> having any 
> > effect on the form submission.
> 
> I do not understand that the <select> inside the <datalist> should not 
> be invalid but why it *has* to be barred from constraint validation? 
> Adding the required attribute to the select element in that case would 
> be stupid and useless. The other way to make the <select> element 
> invalid would be by calling .setCustomValidity(). Is there a real use 
> case that require calling .setCustomValidity() in batch? Even if, can't 
> we rely on the authors not calling .setCustomValidity() on elements that 
> should not be invalid? We already do that for non-displayed elements, 
> don't we?
> 
> You should take into account that this requirement force the UA to check 
> the entire parent tree to prevent a situation that can happen in various 
> other ways.

<select> in a <datalist> is completely ignored for form submission. In 
fact, any form element at all in <datalist> is ignored for form 
submission. See the "construct the form data set" algorithm:

   http://www.whatwg.org/specs/web-apps/current-work/complete.html#constructing-the-form-data-set

It's so that you can do things like:

   <input ... list=options>
   <datalist id=options>
     <select ...>
       <option>...</option>
     </select>
     ...maybe other form controls here...
   </datalist>

Basically everything in the <datalist> except the <option> elements is for 
fallback in legacy UAs and is ignored in new UAs.

-- 
Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'