Duplicative specification of precondition handling

[mnot]

Caching 4.3.2 re-specifies precondition processing from Semantics 13.

E.g.,

A request containing an If-None-Match header field (Section 13.1.2 of [Semantics]) indicates that the client wants to validate one or more of its own stored responses in comparison to whichever stored response is selected by the cache. If the field value is "*", or if the field value is a list of entity-tags and at least one of them matches the entity-tag of the selected stored response, a cache recipient should generate a 304 (Not Modified) response (using the metadata of the selected stored response) instead of sending that stored response.

If an If-None-Match header field is not present, a request containing an If-Modified-Since header field (Section 13.1.3 of [Semantics]) indicates that the client wants to validate one or more of its own stored responses by modification date. A cache recipient should generate a 304 (Not Modified) response (using the metadata of the selected stored response) if one of the following cases is true:

[...]

Do we want to try to fold these into Semantics so that it isn't duplicated? That would require some small adjustments to Semantics AFAICT (e.g., to make it clear what the selected representation is in each case, etc.).

[royfielding]

Why not just end each first sentence with ", as defined in Section X.x of Semantics." and remove the rest?

[royfielding]

Er, never mind ... having looked at the full section, I think this should stay as is because it is refining the requirements in terms of the cache's stored responses.

[royfielding]

I think we can close this. It isn't duplicated: Semantics already refers to this section to define cache handling.

[mnot]

Re-reading the current text, I think I'm finding it most disturbing that semantics 13.1.3 If-Modified-Since doesn't say how to evaluate the condition, whereas caching 4.3.2 does (but just for caches). I think it needs to be removed from caching and made generic.

This is necessary because semantics 13.2 refers to evaluation in their algorithms. INM and if-match define how to evaluate, but IMS and IUS don't.

[royfielding]

I think I'm finding it most disturbing that semantics 13.1.3 If-Modified-Since doesn't say how to evaluate the condition

It defines it near the end of the section because of the etag discussion. Anyway, we can improve that.

[mnot]

I proposed a fix for that, but now that #669 is proposed as well, some of the text in caching is clearly duplicative. Will adjust and push another commit or two; please review.

[royfielding]

There is a larger problem here -- the section on evaluation was split into two sections (evaluation and precedence) but the conditionals only reference the first. This can be fixed by moving precedence back within evaluation with subsections for the other content in evaluation.

[royfielding]

Okay, I have updated the PR to make evaluation one section (with two subsections), fixed a few typos, made the requirements self-descriptive, and updated If-Range to be consistent as well.