[cssom][css-images] CSS.elementSources incompatible with CSS being an IDL namespace

[zcorpan]

From https://www.w3.org/Bugs/Public/show_bug.cgi?id=29623

https://drafts.csswg.org/css-images-4/#elementsources

reads

partial interface CSS {
  [SameObject] readonly attribute Map elementSources;
};

If we switch CSS over to be IDL namespace instead of interface, it can only use operations, not attributes, as far as I can tell.

elementSources is not implemented anywhere, is it? Should we change it to an operation when switching to IDL namespace? Or should namespaces be able to use attributes in Web IDL?

[nox]

AFAICT that specification is wrong anyway, because it's an attribute so CSS should be instantiated first, but then the code snippet said:

CSS.elementSources.set('fancy', bg);

Which clearly is trying to use elementSources has a static attribute.

[zcorpan]

Yep, indeed.

On a related note document.cssElementMap was removed from HTML in whatwg/html#258 (due to lack of implementations for years).

[bzbarsky]

The use of Map here is a concern as well. It causes some implementation issues and couples layout to scripting in ways that are not necessarily desirable. A maplike would make a lot more sense.

Anyway, we could add attribute support to namespaces. We just didn't have any use cases so far, and it's hard to design in a vacuum....

[tabatkins]

Yeah, that spec version is way out of date and needs to get some stuff dropped.