Parsing as Structured Fields: MAY or SHOULD?

[mnot]

Right now, parsing of targeted Cache-Control is specified like this:

Targeted fields MAY be parsed as a Dictionary Structured Field [RFC8941], and implementations are encouraged to use a parser for that format in the interests of robustness, interoperability and security. [...] However, implementers MAY reuse a Cache-Control parser for simplicity.

The idea here is that while we'd like the interop benefits of SF, we recognise that some -- perhaps many -- implementers will have a strong motivation to reuse their Cache-Control parsers.

This seems like it might be the worst of both worlds, in that we now have two possible implementation strategies. Given that there are several SF implementations now, I wonder whether should reconsider this. E.g.,

1. Strengthen the first MAY to a SHOULD, making the field sf-first, or even
2. Require SF, don't allow reuse of CC parsers

[mnot]

Reopening to double-check that we still want to allow CC parsers.

[mnot]

To be clear: the remaining issue (as discussed at the interim) is whether we want to remove the text allowing Cache-Control parsers to be reused for this field.