Standard usage (in general, not just IDs and RFCs) is that if you're
absolutely sure that your intended audience knows what you're talking about,
you can omit the explanation, as I just did. You can also omit explanations
when talking about abbreviations that have made their way into the language
as words in their own right, such as radar or laser, even if your audience
might not know what the "full" version is. The same goes for things
generally known by the abbreviation rather than the full version, such as
MCI or TCP/IP.
If there is any doubt, however, the custom is to put an explanation of the
abbreviation (acronyms being just one kind of abbreviation) after its first
usage within a document. After that, you can use just the acronym. Note
that such doubt can generally be assumed!
If you're only going to refer to it once, you may as well not bother using
the abbreviation at all -- except if you want to make sure that the
abbreviation appears in the document for search purposes (such as on
resumes).
In a document such as an ID/RFC, you also have the luxury of adding
appendices, such as a Glossary, just in case. This is very useful, just in
case someone started in the middle and missed your initial (explained) usage
of the acronym. As someone else pointed out, you can also put it in the
Index -- but the clearest way would be to put in there in both the
abbreviated and full forms.
--
Dave Aronson, Software Engineer, +1-571-434-2039 V, +1-571-434-2001 F.
Cryptek Secure Communications, 1501 Moran Rd., Sterling, VA 20166 USA.
Opinions above are MINE, ALL MINE -- but for rent at reasonable rates.