usefor-article-03 February 2000

4.2.4.  Comments

   Strings of characters which are treated as comments may be included
   in header-contents wherever the syntactic element CFWS occurs. They
   consist of characters enclosed in parentheses. Such strings are
   considered comments so long as they do not appear within a quoted-
   string. Comments may be nested.

   A comment is normally used to provide some human readable
   informational text, except at the end of an address which contains no
   phrase, as in
      fred@foo.bar.example (Fred Bloggs)
   as opposed to
      "Fred Bloggs" <fred@foo.bar.example> .
   The former is a deprecated, but commonly encountered, usage and
   reading agents SHOULD take special note of such comments as
   indicating the name of the person whose address it is. In all other
   situations a comment is semantically interpreted as a single SP.
   Since a comment is allowed to contain FWS, folding is permitted
   within it as well as immediately preceding and immediately following
   it. Also note that, since quoted-pair is allowed in a comment, the
   parenthesis and backslash characters may appear in a comment so long
   as they appear as a quoted-pair. Semantically, the enclosing
   parentheses are not part of the comment content; the content is what
   is contained between the two parentheses.

   Since comments have not hitherto been permitted in news articles,
   except in a few specified places, posters and posting-agents SHOULD
   NOT insert them except in those places, namely following addresses in
   From and similar headers, and to indicate the name of the timezone in
   Date headers.  However, compliant software MUST accept them in all
   places where they are syntactically allowed.