Third, as instructions to registrants, I think it's absolutely fine to say
"you MUST [include this information," and "you SHOULD [include that
information]," and so on. I think that respects the spirit of 2119, in
that things are more likely to interoperate if the documentation of
registered values is up to snuff.
FWIW, my experience with "running code" in this area is that this is a case
where the use of such directive does seem to help. (Assuming, of course, that
the registrant even bothers to read the procedure. Plain text capitalization is
not big enough to catch the attention of those who don't.)
Ned