content-warning: add header considerations

[ioggstream]

I expect

to have header considerations https://tools.ietf.org/html/rfc7231#section-8.3.1 in content-warning spec

Further questions

• [x] which is the behavior of Content-Warning in case of no-content responses eg. HEAD?

• [x] if the "warning" attribute is part of the representation, is that supposed to be returned even by subsequent GET requests? How does this impact with caching? See #138

• [ ] This header SHOULD/NOT be cached/used in CONNECTION / mentioned in Vary

• [x] Intermediaries MUST NOT modify its value. (7fb08fa)

[andrecedik]

I've added a few things to address your points:

• added section for cache considerations (https://github.com/dret/I-D/commit/2af5ba15c1795cce5488d66ad888484f50477364)
• added information about/for intermediaries (https://github.com/dret/I-D/commit/7fb08fac548a45d83d675d1024c5ec1819e03474)

I'm still working on them, so for now this is just an FYI 😉

[ioggstream]

Moved the cache/representation parte in another issue, as I think that's complex.

[andrecedik]

• Added two sections explaining, which HTTP request methods are allowed in combination with the Content-Warning field and the embedded-warning (https://github.com/dret/I-D/commit/a419ba894bad4cd31ae0b16f01adb26fd71161cc)

[ioggstream]

I left a comment on the above commit: https://github.com/dret/I-D/commit/a419ba894bad4cd31ae0b16f01adb26fd71161cc#r39174548