"The template element" content model and <picture>

[zcorpan]

https://html.spec.whatwg.org/multipage/scripting.html#the-template-element

The template element

...should list the content model of picture elements in its own content model. Also update the Elements Index.

[zcorpan]

Currently the author requirements for picture-source only apply if the parent is a picture. Would also need to change that so it works when inside template, or when there's no parent (maybe?).

[zcorpan]

@sideshowbarker how should this work? When source is in template, should template's content model be decided based on the attributes of the first source element? Like, if it has a srcset attribute, use the picture content model; otherwise use the video/audio content model.

[sideshowbarker]

When source is in template, should template's content model be decided based on the attributes of the first source element? Like, if it has a srcset attribute, use the picture content model; otherwise use the video/audio content model.

After thinking about this, that makes sense to me (though I think it’s going to be complicated to implement in the checker). But maybe this is a case where we ideally need some real use cases if we can find them—examples from actual web developers who are using source within template. I wonder if @studdugie might have some feedback on this.

[studdugie]

I have no real feedback yet because we (my shop) have been waiting for the debate on how to do responsive images to produce something usable. But now that there is a spec and an implementation via Chrome 46 of client side hints the picture element now has our attention and we should be putting it into production in the 2nd or 3rd quarter of this year. So anything said before then would not be based on production experience.

[zcorpan]

The template case is made moot by #1502 but there is still an issue of parentless source elements (whose node document has a browsing context) is only allowed to have a type attribute and global attributes. But maybe that's OK. At least until there exist software that checks document conformance for such nodes... Closing this for now.