there's plenty of "running code" in this space - for example, there are
heaven knows how many nonstandard header field in use, but aside from the
attempts by Jacob Palme and other third parties leading up to the current
header registration model, how many independent RFC submissions have
there been by authors seeking to document their header usage?
BTW, RFC 3864 is an _excellent_ model for an "expert review" registry:
It allows to "reserve" header fields with provisional registrations
(example: Archived-At) while they're not yet standardized, it allows
to deprecate non-standard header fields (example: Errors-To), and if
a header field finally makes into an RFC (or similar, but we can ignore
"similar" for status codes), it's added to the "permanent" registry.
With that rules in place the old x.7.8 defined in an I-D could have
been registered provisionally, avoiding the current mess.
Models without a "provisional registry" don't avoid such collisions in
practice, they only avoid the collisions in standards published years