I think the answer is "sometimes". In Content-Disposition filename I'd say
yes. For the name parameter of message/external-body, I'd say yes.
I think the idea of quoted-phrase is fine, I just didn't like the formal
grammar used in the previous Content-Disposition draft. Can we do
something simple like:
quoted-phrase = quoted-string /
<"> encoded-word *(linear-white-space encoded-word) <">
; "Q" encoding can't contain <">, "\" or CR
Then permit quoted-phrase in select value parameters?
This sounds fine to me. I assume that the linear-white-space would be ignored
here, per RFC1522 rules.
Perhaps restrict to 1 character set per quoted-phrase?
This should be up to the parameter to specify. I would restrict file names this
way but not something like an operator message.
One other trick that could be added, is to permit linear-white-space
between the <"> and encoded-words, but require that it be ignored.
The advantage to this is that current 1522 clients using rule (1) from
section 6.1 for unknown header fields would decode the encoded-words
for display. The disadvantage (which probably rules it out) is that
current Content-Disposition implementations would end up with
filenames that would confuse users.
I think the disadvantage outweighs the advantage, but I could be convinced