[web-animations-1] Document associations for document timelines

[jakearchibald]

The default document timeline should be for="document" since they're per document.

Document timelines should have a <dfn for="document timeline">document</dfn> so their association is properly defined.

[jakearchibald]

I don't think that fix is quite right. Now "the timeline has a default document timeline", which doesn't seem right. It feels like it should be "the document has a default timeline".

And "the document timeline has a document".

[birtles]

Yes sorry, you're right! I made that change in a real hurry this morning since I'll be away next week and I wanted to take care of this first.

[jakearchibald]

I'm happy to get a PR together. I realise I'm being the fussy one 😄