Charles Lindsey writes:
And (AIUI) it contains just whatever Dan thinks it ought, or ought
not, to contain.
The point of http://cr.yp.to/immhf.html, http://cr.yp.to/smtp.html, etc.
is interoperability. An accidental conflict of header field names is an
interoperability problem. An open list, properly used, eliminates this
problem.
If you actually look at the list, you'll see more than 100 field names,
not counting all the different Resent-* names, which are described as a
single syntactic rule. You'll see X-X-Sender even though Pine's use of
that field is a truly horrible idea.
---Dan