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- Newsgroups: comp.mail.headers
- Path: sparky!uunet!gatech!ukma!widener!eff!ckd
- From: ckd@eff.org (Christopher Davis)
- Subject: Re: X-FOOBAR: style headers (What are they?)
- In-Reply-To: pwl@tc.fluke.COM's message of 21 Jul 92 16:06:03 GMT
- Message-ID: <CKD.92Jul21170744@loiosh.eff.org>
- Sender: usenet@eff.org (NNTP News Poster)
- Nntp-Posting-Host: loiosh.eff.org
- Organization: Electronic Frontier Foundation Tech Central
- References: <1992Jul21.160603.4774@tc.fluke.COM>
- Date: Tue, 21 Jul 1992 21:09:53 GMT
- Lines: 46
-
- Paul> == Paul Lutt <pwl@tc.fluke.COM>
-
- Paul> While not a newcomer to email or netnews, I'm a bit confused about the
- Paul> origin and use of email headers of the form:
-
- Paul> X-FOOBAR:
-
- Paul> Where FOOBAR may be some commonly used header field, such as
- Paul> FROM.
-
- Paul> I've looked through the RFCs that we have locally and can find no
- Paul> mention of this practice. Could some kind soul please enlighten me?
- Paul> Thanks.
-
- RFC822:
- 4.7.4. EXTENSION-FIELD
-
- A limited number of common fields have been defined in
- this document. As network mail requirements dictate, addi-
- tional fields may be standardized. To provide user-defined
- fields with a measure of safety, in name selection, such
- extension-fields will never have names that begin with the
- string "X-".
-
- 4.7.5. USER-DEFINED-FIELD
-
- Individual users of network mail are free to define and
- use additional header fields. Such fields must have names
- which are not already used in the current specification or in
- any definitions of extension-fields, and the overall syntax of
- these user-defined-fields must conform to this specification's
- rules for delimiting and folding fields. Due to the
- extension-field publishing process, the name of a user-
- defined-field may be pre-empted
-
- Note: The prefatory string "X-" will never be used in the
- names of Extension-fields. This provides user-defined
- fields with a protected set of names.
-
- Basically, that means a simple and guaranteed method of "commenting out"
- a header is to add "X-" to the beginning.
- --
- Christopher Davis * ckd@eff.org * System Administrator, EFF * +1 617 864 0665
- ``The First Amendment is often inconvenient. But that is besides the
- point. Inconvenience does not absolve the government of its obligation
- to tolerate speech.'' --Justice Anthony Kennedy, in 91-155
-