Reaction: Indicating Summary Reaction to a Message

Document Type Active Internet-Draft (individual in art area)
Authors Dave Crocker  , R. Signes  , Ned Freed 
Last updated 2021-05-12 (latest revision 2021-04-16)
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Network Working Group                                         D. Crocker
Internet-Draft                               Brandenburg InternetWorking
Intended status: Experimental                                  R. Signes
Expires: October 18, 2021                                       Fastmail
                                                                N. Freed
                                                          April 16, 2021

           Reaction: Indicating Summary Reaction to a Message


   The popularity of social media has led to user comfort with easily
   signaling basic reactions to an author's posting, such as with a
   'thumbs up' or 'smiley' graphic.  This specification permits a
   similar facility for Internet Mail.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 18, 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Reaction Content-Disposition  . . . . . . . . . . . . . . . .   3
   4.  Reaction Message Processing . . . . . . . . . . . . . . . . .   5
   5.  Usability Considerations  . . . . . . . . . . . . . . . . . .   6
     5.1.  Example Message . . . . . . . . . . . . . . . . . . . . .   6
     5.2.  Example Display . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  Experimental Goals  . . . . . . . . . . . . . . . . . . . . .   8
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   9
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   The popularity of social media has led to user comfort with easily
   signaling summary reactions to an author's posting, by using emoji
   graphics, such as with a 'thumbs up', 'heart', or 'smiley'
   indication.  Sometimes the permitted repertoire is constrained to a
   small set and sometimes a more extensive range of indicators is

   This specification extends this existing practice in social media and
   instant messaging into Internet Mail.

   While it is already possible to include symbols and graphics as part
   of an email reply's content, there has not been an established means
   of signalling the semantic substance that such data are to be taken
   as a summary 'reaction' to the original message.  That is, a
   mechanism to identify symbols as specifically providing a summary
   reaction to the cited message, rather than merely being part of the
   free text in the body of a response.  Such a structured use of the
   symbol(s) allows recipient MUAs to correlate this reaction to the
   original message and possibly to display the information

   This facility defines a new MIME Content-Disposition, to be used in
   conjunction with the In-Reply-To header field, to specify that a part
   of a message containing one or more emojis can be be treated as a
   summary reaction to a previous message.

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2.  Terminology

   Unless provided here, terminology, architecture and specification
   notation used in this document are incorporated from:

   o  [Mail-Arch]

   o  [Mail-Fmt]

   o  [MIME]

   , and syntax is specified with

   o  [ABNF]

   The ABNF rule Emoji-Seq is inherited from [Emoji-Seq]; details are in
   Section 3.

   Normative language, per [RFC8174]:

      The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
      "MAY", and "OPTIONAL" in this document are to be interpreted as
      described in BCP 14 [RFC2119] [RFC8174] when, and only when, they
      appear in all capitals, as shown here.

3.  Reaction Content-Disposition

   A message sent as a reply MAY include a part containing:

   Content-Disposition: reaction

   If such a field is specified the Content-Type of the part MUST be:

   Content-Type: text/plain; charset=utf-8

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   The content of this part is restricted to a single line of emoji.
   The [ABNF] is:

   part-content    = emoji *(WSP emoji) CRLF

   emoji           = emoji-sequence
   emoji-sequence  = { defined in [Emoji-Seq] }

   base-emojis     = thumbs-up / thumbs-down / grinning-face /
                     frowning-face / crying-face

   thumbs-up       = {U+1F44D}
   thumbs-down     = {U+1F44E}
   grinning-face   = {U+1F600}
   frowning-face   = {U+2639}
   crying-face     = {U+1F622}

   The part-content is either the entire content portion of a message's
   single MIME body or it is the content portion of the first MIME
   multi-part body-part that constitute a message's body.

   The ABNF rule emoji_sequence is inherited from [Emoji-Seq].  It
   defines a set of Unicode code point sequences, which must then be
   encoded as UTF-8.  Each sequence forms a single pictograph.  The BNF
   syntax used in [Emoji-Seq] differs from [ABNF], and MUST be
   interpreted as used in Unicode documentation.  The referenced
   document describes these as sequences of code points.

   Note:    The part-content can first be parsed into candidate
      reactions, separated by WSP.  Each candidate reaction that does
      not constitute a single emoji-sequence (as per [Emoji-Seq]) is
      invalid.  Invalid candidates can be treated individually, rather
      than affecting the remainder of the part-content's processing.
      The remaining candidates form the set of reactions to be
      processed.  This approach assumes use of a mechanism for emoji
      sequence validation that is not specified here.

   The rule base-emojis is provided as a simple, common list, or
   'vocabulary' of emojis, It was developed from some existing practice,
   in social networking, and is intended for similar use.  However
   support for it as a base vocabulary is not required.  Having
   providers and consumers employ a common set will facilitate user
   interoperability, but different sets of users might want to have
   different, common (shared) sets.

   The reaction emoji(s) are linked to the current message's In-Reply-
   To: field, which references an earlier message, and provides a

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   summary reaction to that earlier message.  [Mail-Fmt].  For
   processing details, see Section 4.

   Reference to unallocated code points SHOULD NOT be treated as an
   error; the corresponding UTF-8 encoded code points SHOULD be
   processed using the system default method for denoting an unallocated
   or undisplayable code point.

   Note:    The "emoji" token looks simple.  It isn't.  Implementers are
      well-advised not to assume that emoji sequences are trivial to
      parse or validate.  Among other concerns, an implementation of the
      Unicode Character Database is required.  An emoji is more than a
      stand-in for a simple alternation of characters.  Similarly, one
      emoji sequence is not interchangeable with, or equivalent to,
      another one, and comparisons require detailed understanding of the
      relevant Unicode mechanisms.  Use of an existing Unicode
      implementation will typically prove extremely helpful, as will an
      understanding of the error modes that may arise with a chosen

4.  Reaction Message Processing

   The presentation aspects of reaction processing are necessarily MUA-
   specific and beyond the scope of this specification.  In terms of the
   message itself, a recipient MUA that supports this mechanism operates
   as follows:

   1.  If a received message R's header contains an In-Reply-To: field,
       check to see if it references a previous message that the MUA has
       sent or received.

   2.  If R's In-Reply-To: does reference one, then check R's message
       content for a part with a "reaction" Content-Disposition header
       field, at either the outermost level or as part of a multipart at
       the outermost level.

   3.  If such a part is found, and the content of the part conforms to
       the restrictions outlined above, remove the part from the message
       and process the part as a reaction.

   Note:    A message's content might include other, nested messages.
      These can be analyzed for reactions, independently of the
      containing message, applying the above algorithm for each
      contained message, separately.

   Again, the handling of a message that has been successfully processed
   is MUA-specific and beyond the scope of this specification.

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5.  Usability Considerations

   This specification defines a mechanism for the structuring and
   carriage of information.  It does not define any user-level details
   of use.  However the design of the user-level mechanisms associated
   with this facility is paramount.  This section discusses some issues
   to consider.

   Creation:    Because an email environment is different from a typical
      social media platform, there are significant -- and potentially
      challenging -- choices in the design of the user interface, to
      support indication of a reaction.  Is the reaction to be sent only
      to the original author, or should it be sent to all recipients?
      Should the reaction always be sent in a discrete message
      containing only the reaction, or should the user also be able to
      include other message content?  (Note that carriage of the
      reaction in a normal email message enables inclusion of this other

   Display:    Reaction indications might be more useful when displayed
      in close visual proximity to the original message, rather than
      merely as part of an email response thread.  The handling of
      multiple reactions, from the same person, is also an opportunity
      for possibly interesting user experience design choice.

   Culture:    The use of an image, intended to serve as a semantic
      signal, is determined and affected by cultural factors, which
      differ in complexity and nuance.  It is important to remain aware
      that an author's intent when sending a particular emoji might not
      match how the recipient interprets it.  Even simple, commonly used
      emojis can be be subject to these cultural differences.

5.1.  Example Message

   A simple message exchange might be:

   Date: Today, 29 February 2021 00:00:00 -800
   Subject: Meeting

   Can we chat at 1pm pacific, today?

   with a thumbs-up, affirmative response of:

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   Date: Today, 29 February 2021 00:00:10 -800
   Subject: Meeting
   Mime-Version: 1.0 (1.0)
   Content-Type: text/plain; charset=utf-8
   Content-Disposition: Reaction


   The Unicode character, represented here as "{U+1F44E}" for
   readability, would actually be sent as the UTF-8-encoded character.

   The example could, of course, be more elaborate, such as the first of
   a MIME multipart sequence.

5.2.  Example Display

   Repeating the caution that actual use of this capability requires
   careful usability design and testing, this section describes simple
   examples -- which have not been tested -- of how the reaction
   response might be displayed in a summary list of messages :

   Summary:    Summary listings of messages in a folder include columns
      such as Subject, From, and Date.  Another might be added, to show
      common reactions and a count of how many of them have been

   Message:    A complete message is often displayed with a tailored
      section for header-fields, enhancing the format and showing only
      selected header fields.  A pseudo-field might be added, for
      reactions, again showing the symbol and a count.

6.  Security Considerations

   This specification employs message content that is a strict subset of
   existing possible content, and thus introduces no new content-
   specific security considerations.  The fact that this content is
   structured might seem to make it a new threat surface, but there is
   no analysis demonstrating that it does.

   This specification defines a distinct Content-Disposition value, for
   specialized message content.  Processing that handles the content
   differently from other content in the message body might introduce
   vulnerabilities.  Since this capability is likely to produce new user

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   interaction features, that might also produce new social engineering

7.  IANA Considerations

   The IANA is requested to register the Reaction MIME Content-
   Disposition parameter, per [RFC2183]

    Content-Disposition parameter name:    reaction

   Allowable values for this parameter:    (none)

    Description:   Permit a recipient to respond by signaling basic
      reactions to an author's posting, such as with a 'thumbs up' or
      'smiley' graphic

8.  Experimental Goals

   The basic, email-specific mechanics for this capability are well-
   established and well-understood.  Points of concern, therefore, are:

   o  Technical issues in using emojis within a message body part

   o  Market interest

   o  Usability

   So the questions to answer for this Experimental specification are:

   o  Is there demonstrated interest by MUA developers?

   o  If MUA developers add this capability, is it used by authors?

   o  Does the presence of the Reaction capability create any
      operational problems for recipients?

   o  Does the presence of the Reaction capability demonstrate
      additional security issues?

   o  What specific changes to the specification are needed?

   o  What other comments will aid in use of this mechanism?

   Please send comments to

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9.  Normative References

   [ABNF]     Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 5234, January 2008.

              Davis, M., Ed. and P. Edberg., Ed., "Unicode(R) Technical
              Standard #51: Unicode Emoji", WEB
              September 2020.

              Crocker, D., "Internet Mail Architecture", RFC 5598, July

              Resnick, P., Ed., "Internet Message Format", RFC 5322,
              October 2008.

   [MIME]     Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

   [RFC2183]  Troost, R., Dorner, S., and K. Moore, Ed., "Communicating
              Presentation Information in Internet Messages: The
              Content-Disposition Header Field", RFC 2183,
              DOI 10.17487/RFC2183, August 1997,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

Appendix A.  Acknowledgements

   This specification had substantive commentary on three IETF mailing

   This work began as a private exercise, in July 2020, with private
   discussion, for draft-crocker-reply-emoji.  It morphed into draft-
   crocker-inreply-react, with significant discussion on the ietf-822
   mailing list, September through November 2020.  The discussion
   produced a fundamental change from proposing a new header field to
   instead defining a new Content-Disposition type, as well as
   significantly enhancing its text concerning Unicode.  It also
   produced two additional co-authors.

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   In November 2020, the Dispatch list was queried about the draft, but
   produced no discussion, though it did garner one statement of

   A 4-week Last Call was issued on the document, January 2021,
   resulting in quite a bit of fresh discussion on the last-call mailing
   list, and producing further changes to the draft.  After Last Call
   completed, additional concerns were surfaced, about the Unicode-
   related details, producing yet more changes to the draft.  It also
   produced a challenge that prompted the current version of the
   Acknowledgements section.

   Readers who are interested in the detail of the document's history
   are encouraged to peruse the archives for the three lists, searching
   Subject fields for "-react".

Authors' Addresses

   Dave Crocker
   Brandenburg InternetWorking


   Ricardo Signes


   Ned Freed


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