Restrict the types of nodes that could be assigned to a slot

[rniwa]

It seems that we only want Text and Element nodes to be assigned to a slot. There is currently no mechanism to assign non-element nodes to a slot other than via the default slot so this is only relevant to default slots. Since only Text and Element nodes are visible, we can probably not even expose assignedSlot on non-Text CharacterData nodes.

[rniwa]

@annevk @travisleithead @hayatoito

[hayatoito]

I do not have a strong opinion on this. This sounds a minor issue and does not cause a real issue, IMO.

Do we really want to introduce this restriction? I'm fine that non-Text CharacterData is assigned to a slot, which is harmless.

If we want to introduce the restriction, that's easy, I think. We have to:

1. Change the IDL

From:

partial interface NonDocumentTypeChildNode {
    readonly        attribute HTMLSlotElement? assignedSlot;
};

To:

partial interface Element {
    readonly        attribute HTMLSlotElement? assignedSlot;
};

partial interface TextNode {
    readonly        attribute HTMLSlotElement? assignedSlot;
};

1. Tweak the slotting algorithm in the spec. Additional one sentence is enough.
2. UA has to introduce "if () { } else {}" in implementing slotting algorithm . :)

[rniwa]

This actually reduces the amount of code needed in our engine (WebKit) so it's highly desirable for us.

[hayatoito]

Okay. Then, it is worth doing. I'm okay to this minor change.

Out of curiosity, could you have a chance to share your experience briefly? Why does this change impact WebKit? I've not encountered such an issue in Blink. I'm afraid that I might have missed something.

[rniwa]

It's something to do with the way our style resolution works, and that has changed quite a bit between Blink and WebKit since Blink fork so I'm not certain how relevant our issue is.

[hayatoito]

I got it. Thanks.