The Text/Plain Format Parameter
RFC 2646

Document Type RFC - Proposed Standard (August 1999; No errata)
Obsoleted by RFC 3676
Updates RFC 2046
Was draft-gellens-format (individual)
Last updated 2013-03-02
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Network Working Group                                 R. Gellens, Editor
Request for Comments: 2646                                      Qualcomm
Updates: 2046                                                August 1999
Category: Standards Track

                    The Text/Plain Format Parameter

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

Table of Contents

    1.  Abstract . . . . . . . . . . . . . . . . . . . . . . . . . .  2
    2.  Conventions Used in this Document . . . . . . . . . . . . .   2
    3.  The Problem  . . . . . . . . . . . . . . . . . . . . . . . .  2
      3.1.  Paragraph Text  . . . . . . . . . . . . . . . . . . . .   3
      3.2.  Embarrassing Line Wrap . . . . . . . . . . . . . . . . .  3
      3.3.  New Media Types . . . . . . . . . . . . . . . . . . . .   4
    4.  The Format Parameter to the Text/Plain Media Type  . . . . .  4
      4.1.  Generating Format=Flowed  . . . . . . . . . . . . . . .   5
      4.2.  Interpreting Format=Flowed . . . . . . . . . . . . . . .  6
      4.3.  Usenet Signature Convention . . . . . . . . . . . . . .   7
      4.4.  Space-Stuffing . . . . . . . . . . . . . . . . . . . . .  7
      4.5.  Quoting . . . . . . . . . . . . . . . . . . . . . . . .   8
      4.6.  Digital Signatures and Encryption  . . . . . . . . . . .  9
      4.7.  Line Analysis Table . . . . . . . . . . . . . . . . . .  10
      4.8.  Examples . . . . . . . . . . . . . . . . . . . . . . . . 10
    5.  ABNF  . . . . . . . . . . . . . . . . . . . . . . . . . . .  11
    6.  Failure Modes  . . . . . . . . . . . . . . . . . . . . . . . 11
      6.1.  Trailing White Space Corruption . . . . . . . . . . . .  11
    7.  Security Considerations  . . . . . . . . . . . . . . . . . . 12
    8.  IANA Considerations . . . . . . . . . . . . . . . . . . . .  12
    9.  Internationalization Considerations  . . . . . . . . . . . . 12
   10.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . .  12
   11.  References . . . . . . . . . . . . . . . . . . . . . . . . . 13
   12.  Editor's Address  . . . . . . . . . . . . . . . . . . . . .  13
   13.  Full Copyright Statement . . . . . . . . . . . . . . . . . . 14

Gellens                     Standards Track                     [Page 1]
RFC 2646            The Text/Plain Format Parameter          August 1999

1.  Abstract

   Interoperability problems have been observed with erroneous labelling
   of paragraph text as Text/Plain, and with various forms of
   "embarrassing line wrap." (See section 3.)

   Attempts to deploy new media types, such as Text/Enriched [RICH] and
   Text/HTML [HTML] have suffered from a lack of backwards compatibility
   and an often hostile user reaction at the receiving end.

   What is required is a format which is in all significant ways
   Text/Plain, and therefore is quite suitable for display as
   Text/Plain, and yet allows the sender to express to the receiver
   which lines can be considered a logical paragraph, and thus flowed
   (wrapped and joined) as appropriate.

   This memo proposes a new parameter to be used with Text/Plain, and,
   in the presence of this parameter, the use of trailing whitespace to
   indicate flowed lines.  This results in an encoding which appears as
   normal Text/Plain in older implementations, since it is in fact
   normal Text/Plain.

2.  Conventions Used in this Document

   The key words "REQUIRED", "MUST", "MUST NOT", "SHOULD", "SHOULD NOT",
   and "MAY" in this document are to be interpreted as described in "Key
   words for use in RFCs to Indicate Requirement Levels" [KEYWORDS].

3.  The Problem

   The Text/Plain media type is the lowest common denominator of
   Internet email, with lines of no more than 997 characters (by
   convention usually no more than 80), and where the CRLF sequence
   represents a line break [MIME-IMT].

   Text/Plain is usually displayed as preformatted text, often in a
   fixed font.  That is, the characters start at the left margin of the
   display window, and advance to the right until a CRLF sequence is
   seen, at which point a new line is started, again at the left margin.
   When a line length exceeds the display window, some clients will wrap
   the line, while others invoke a horizontal scroll bar.

   Text which meets this description is defined by this memo as "fixed".

   Some interoperability problems have been observed with this media
   type:

Gellens                     Standards Track                     [Page 2]
RFC 2646            The Text/Plain Format Parameter          August 1999

3.1.  Paragraph Text
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