Just require id for everything and be done with it

[azaroth42]

Only embedded AnnotationPages do not require id, and instead they're SHOULD, as per http://iiif.io/api/presentation/3.0/#id

We should just make id a MUST for consistency. The exception here is pointless and will catch implementers out.

[tomcrane]

If id required for everything, could then have simpler (tabular?) guidance on dereferenceability and whether the form of the id must be http... or whether it can be #document-relative

Replace Protocol behaviour table with two cols: | deref | allow # | ?

[azaroth42]

Community call 2018-08-01: Makes sense. One exception is worse than not requiring it. Need to be clear that it doesn't require dereferencing.

[azaroth42]

Closed by #1648

[zimeon]

Approved by TRC, already merged into image-prezi-rc2.