Add attributeFilter

[domenic]

At defineElement time,

1. Do a Get(PassedConstructor, "attributeFilter").
2. If it is undefined,
   1. never queue attribute changed callbacks
   2. if attributeChangedCallback is present, throw a "what are you doing?" error
3. Run the Web IDL "convert to sequence<DOMString>" algorithm on it, rethrowing any errors
4. Store the resulting sequence as the attribute filter and use it to dispatch attributeChangedCallbacks.

There's no provision in v1 for "all attributes".

[hayatoito]

Bikeshed: Can we avoid to use the term of 'filter' in attributeFilter?
Because "never queue attribute changed callbacks" is now the default behavior, 'filter' sounds weird to me.

observedAttributes or something might be better.

[hayatoito]

I found that the term of attributeFilter is used also in MutationObserver. Then, it might make sense for consistency. :)

[domenic]

I understand the confusion; a filter makes more sense when the default is to allow all. I am OK with observedAttributes. @annevk, @rniwa, any thoughts?

[chaals]

observedAttributes does sound like a clear explanation that "this is where the bikes go"… (is observeAttributes clearer, or just serious bikeshedding?)

[rniwa]

observedAttributes does sound like a clear explanation that "this is where the bikes go"… (is observeAttributes clearer, or just serious bike shedding?)

I don't think it should be a verb given it's a property.

[domenic]

Went with observedAttributes in 3286f00. Relevant sections:

• https://w3c.github.io/webcomponents/spec/custom/#extensions-to-document-interface-to-register step 10 and 11.
• https://w3c.github.io/webcomponents/spec/custom/#dfn-enqueue-lifecycle-callback step 6