Protocol examples should use comma separated headers in examples

[azaroth42]

Given that many implementations use a dictionary approach to sending and receiving headers, having multiple headers with the same name will result in data loss, compared to using comma separated values in a single header.

For example the link headers: https://www.w3.org/TR/annotation-protocol/#responses-without-annotations

Plus add a note explaining the rationale.

Discussed: http://www.w3.org/2016/07/29-annotation-irc#T15-45-55

[BigBlueHat]

@azaroth42 thoughts?
a6b358e

[azaroth42]

Looks good. I might combine the second and third paragraphs?

[BigBlueHat]

So...we have a new problem...from RFC 7230 (bottom of page 5):

   To avoid any possible ambiguity, individual preference tokens SHOULD
   NOT appear multiple times within a single request.  If any preference
   is specified more than once, only the first instance is to be
   considered.  All subsequent occurrences SHOULD be ignored without
   signaling an error or otherwise altering the processing of the
   request.  This is the only case in which the ordering of preferences
   within a request is considered to be significant.

If I'm reading that correctly, the way we're using Prefer doesn't work...as the last value "wins" meaning the server can't really use them both together. (Proposal for fixing forthcoming).

[BigBlueHat]

So I had this wonderful proposal for fixing this, but just found that it looks like LDP just provides multiple include values as space delimited IRIs:

From: https://www.w3.org/TR/ldp/#prefer-examples-direct-membershiponly

Clients interested only in information about the container (for example, which membership predicate it uses) and its membership might use this hint on a GET request: Prefer: return=representation; include="http://www.w3.org/ns/ldp#PreferMembership http://www.w3.org/ns/ldp#PreferMinimalContainer".

include is not (as yet) a registered preference, so perhaps we'll need more information added to my note commit that explains its usage. And perhaps we should help LDP (or whoever) get include registered.

Thoughts?

[BigBlueHat]

Here's the LDP-level definition of the include parameter for Prefer:
https://www.w3.org/TR/ldp/#h-prefer-include