rfc2822 April 2001

4.1. Miscellaneous obsolete tokens

   These syntactic elements are used elsewhere in the obsolete syntax or
   in the main syntax.  The obs-char and obs-qp elements each add ASCII
   value 0. Bare CR and bare LF are added to obs-text and obs-utext.
   The period character is added to obs-phrase. The obs-phrase-list
   provides for "empty" elements in a comma-separated list of phrases.

   Note: The "period" (or "full stop") character (".") in obs-phrase is
   not a form that was allowed in earlier versions of this or any other
   standard.  Period (nor any other character from specials) was not
   allowed in phrase because it introduced a parsing difficulty
   distinguishing between phrases and portions of an addr-spec (see
   section 4.4).  It appears here because the period character is
   currently used in many messages in the display-name portion of
   addresses, especially for initials in names, and therefore must be
   interpreted properly.  In the future, period may appear in the
   regular syntax of phrase.

obs-qp          =       "\" (%d0-127)

obs-text        =       *LF *CR *(obs-char *LF *CR)
obs-char        =       %d0-9 / %d11 /          ; %d0-127 except CR and
              %d12 / %d14-127         ;  LF

obs-utext       =       obs-text

obs-phrase      =       word *(word / "." / CFWS)

obs-phrase-list =       phrase / 1*([phrase] [CFWS] "," [CFWS]) [phrase]

   Bare CR and bare LF appear in messages with two different meanings.
   In many cases, bare CR or bare LF are used improperly instead of CRLF
   to indicate line separators.  In other cases, bare CR and bare LF are
   used simply as ASCII control characters with their traditional ASCII
   meanings.