Re: Message signatures, structured fields and ABNF

Hi folks,

Mark wrote:
> The point of Structured Fields is that they're not strings, conceptually -- they're data structures.
> Eventually, we might come up with a simple schema language for them,
> but for now prose should be adequate

In this PR we tried to align with the latest  http admin editorial guidelines
defining concepts like quota-policy as data structures and reusing them in
fields.

- https://github.com/ietf-wg-httpapi/ratelimit-headers/pull/90

Editorial feedback is very welcome, since this work can be useful
even in other specs.

Thx++,
R & A