s-o-1036 June 1994

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.)