[whatwg] [selectors4] drag-and-drop pseudo-classes

[Tab Atkins Jr.]

On Mon, Aug 13, 2012 at 11:55 PM, Ryosuke Niwa <rniwa at webkit.org> wrote:
> On Mon, Aug 13, 2012 at 9:19 PM, fantasai <fantasai.lists at inkedblade.net>wrote:
>> The CSSWG discussed drag-and-drop pseudo-classes today. The current
>> proposal is to have three pseudo-classes:
>>
>>   * One for the element representing the drop target that
>>     would receive the item if it were dropped.
>>   * One for all elements representing possible drop targets
>>     that could receive the item.
>
> How do we find these elements? On one hand, if we're only supporting
> dropzone attribute, then adding new pseudo element seems unnecessary. On
> the other hand, I can't think of ways to detect whether an element could
> return false or prevents the default action on dragover/dragenter events
> without firing those events.

Just using [dropzone], yes.

We're not adding a pseudo-element, we're adding pseudo-classes.

I'm not sure how we can possibly do these without pseudo-classes.  Can
you outline what you think it would be?  We have to (a) only trigger
these pseudo-classes while a drag is happening, and (b) trigger the
valid/invalid distinction based on what type was declared in JS or
assumed by OS-level data for the dragged thing.

As well, the pseudo that matches "the drop target that will be used if
you dropped right now" might not be expressible in pure CSS even given
the above.  It's probably equivalent to "when you :hover it", but
there are applications that basically have this functionality that
work differently - for example, I think that the built-in Windows
solitaire game highlight the closest drop target to the current mouse
pointer, even if you're nowhere near the actual drop zone.

~TJ