usefor-article-03 February 2000

4.2.3.  White Space and Continuations

[The following text is taken from [MESSFOR], adapted to the different
terminology used for this standard.]

   Each header is logically a single line of characters comprising the
   header-name, the colon with its following SP, and the header-content.
   For convenience, however, the header-content can be split into a
   multiple line representation; this is called "folding". The general
   rule is that wherever this standard allows for FWS or CFWS (but not
   simply SP or HTAB) a CRLF may be inserted before any WSP. For
   example, the header:
      Approved: modname@modsite.example (Moderator of comp.foo.bar)
   can be represented as:
      Approved: modname@modsite.example
         (Moderator of comp.foo.bar)

        NOTE: Though header-contents are defined in such a way that
        folding can take place between many of the lexical tokens (and
        even within some of them), folding SHOULD be limited to placing
        the CRLF at higher-level syntactic breaks, and SHOULD also avoid
        leaving trailing WSP on the preceding line. For instance, if a
        header-content is defined as comma-separated values, it is
        recommended that folding occur after the comma separating the
        structured items, even if it is allowed elsewhere.

   Folding MUST NOT be carried out in such a way that any line of a
   header is made up entirely of WSP characters and nothing else.

   The colon following the header name on the first line MUST be
   followed by a WSP, even if the header is empty. If the header is not
   empty, at least some of the content MUST appear on the first line
   (this is to avoid the possibility of harm by any non-compliant agent
   that might eliminate a trailing SP). Posting agents MUST enforce
   these restrictions, but relaying agents SHOULD accept even articles
   that violate them.

        NOTE: This standard differs from [MESSFOR] in requiring that WSP
        followng the colon (it was also an [RFC 1036] requirement).

   Posters and posting agents SHOULD use SP, not HTAB, where white space
   is desired in headers (some existing software expects this), and MUST
   use SP immediately following the colon after a header-name. Relaying
   agents SHOULD accept HTAB in all such cases, however.

   Since the white space beginning a continuation line remains a part of
   the logical line, headers can be "broken" into multiple lines only at
   FWS or CFWS. Posting agents SHOULD NOT break headers unnecessarily
   (but see 4.5).

--- ../s-o-1036/White_Space_and_Continuations.out          June 1994
+++ ../usefor-article-03/White_Space_and_Continuations.out          February 2000
@@ -1,47 +1,50 @@
 4.2.3. White Space and Continuations
 
-The  colon  following the header name on the start-line MUST
-be followed by white space, even if the header is empty.  If
-the  header  is not empty, at least some of the content MUST
-appear on the start-line.  Posting agents MUST enforce these
-restrictions,  but  relayers (etc.) SHOULD accept even arti-
-cles that violate them.
-
-     NOTE: MAIL does not require white space after  the
-     colon,  but  it  is  usual.  RFC 1036 required the
-     white space,  even  in  empty  headers,  and  some
-     existing   software  demands  it.   In  MAIL,  and
-     arguably in RFC  1036  (although  the  wording  is
-     vague), it is technically legitimate for the white
-     space to be part of  a  continuation  line  rather
-     than the start-line, but not all existing software
-     will accept  this.   Deleting  empty  headers  and
-     placing some content on the start-line avoids this
-     issue...  which  is  desirable  because   trailing
-     blanks,  easily  deleted by accident, are best not
-
-INTERNET DRAFT to be        NEWS                  sec. 4.2.3
-
-
-     made significant in headers.
-
-In general, posters and  posting  agents  SHOULD  use  blank
-(ASCII  32), not tab (ASCII 9), where white space is desired
-in headers.  Existing software does not consistently  accept
-tab  as  synonymous with blank in all contexts.  In particu-
-lar, RFC 1036 appeared to specify that the character immedi-
-ately  following  the colon after a header name was required
-to be a blank, and some news software insists  on  that,  so
-this  character MUST be a blank.  Again, posting agents MUST
-enforce these restrictions but relayers SHOULD be more  tol-
-erant.
-
-Since  the white space beginning a continuation line remains
-a part of the logical line, headers  can  be  "broken"  into
-multiple  lines  only at white space.  Posting agents SHOULD
-not break headers unnecessarily.  Relayers  SHOULD  preserve
-existing header breaks, and SHOULD not introduce new breaks.
-Breaking headers SHOULD be a last resort; relayers and read-
-ing agents SHOULD handle long header lines gracefully.  (See
-the discussion of size limits in section 4.6.)
+[The following text is taken from [MESSFOR], adapted to the different
+terminology used for this standard.]
+
+   Each header is logically a single line of characters comprising the
+   header-name, the colon with its following SP, and the header-content.
+   For convenience, however, the header-content can be split into a
+   multiple line representation; this is called "folding". The general
+   rule is that wherever this standard allows for FWS or CFWS (but not
+   simply SP or HTAB) a CRLF may be inserted before any WSP. For
+   example, the header:
+      Approved: modname@modsite.example (Moderator of comp.foo.bar)
+   can be represented as:
+      Approved: modname@modsite.example
+         (Moderator of comp.foo.bar)
+
+        NOTE: Though header-contents are defined in such a way that
+        folding can take place between many of the lexical tokens (and
+        even within some of them), folding SHOULD be limited to placing
+        the CRLF at higher-level syntactic breaks, and SHOULD also avoid
+        leaving trailing WSP on the preceding line. For instance, if a
+        header-content is defined as comma-separated values, it is
+        recommended that folding occur after the comma separating the
+        structured items, even if it is allowed elsewhere.
+
+   Folding MUST NOT be carried out in such a way that any line of a
+   header is made up entirely of WSP characters and nothing else.
+
+   The colon following the header name on the first line MUST be
+   followed by a WSP, even if the header is empty. If the header is not
+   empty, at least some of the content MUST appear on the first line
+   (this is to avoid the possibility of harm by any non-compliant agent
+   that might eliminate a trailing SP). Posting agents MUST enforce
+   these restrictions, but relaying agents SHOULD accept even articles
+   that violate them.
+
+        NOTE: This standard differs from [MESSFOR] in requiring that WSP
+        followng the colon (it was also an [RFC 1036] requirement).
+
+   Posters and posting agents SHOULD use SP, not HTAB, where white space
+   is desired in headers (some existing software expects this), and MUST
+   use SP immediately following the colon after a header-name. Relaying
+   agents SHOULD accept HTAB in all such cases, however.
+
+   Since the white space beginning a continuation line remains a part of
+   the logical line, headers can be "broken" into multiple lines only at
+   FWS or CFWS. Posting agents SHOULD NOT break headers unnecessarily
+   (but see 4.5).