Internet Month-Name Date Format (IMDF)
draft-henlich-imdf-00

Internet Engineering Task Force                               T. Henlich
Internet-Draft                                       Henlich Engineering
Intended status: Informational                            24 August 2026
Expires: 25 February 2027

                 Internet Month-Name Date Format (IMDF)
                         draft-henlich-imdf-00

Abstract

   This document defines the Internet Month-Name Date Format (IMDF), a
   concise date representation for English-language human communication.

   IMDF requires an alphabetic month abbreviation.  This makes the month
   visually distinct from the numeric day and reduces errors caused by
   differing regional date-order conventions.

   The specification primarily defines how IMDF dates are presented.  It
   establishes a preferred output form and permits a limited set of
   familiar English-language variants.  Detailed input handling is
   outside its scope.

   IMDF does not replace ISO 8601 for machine interchange, language-
   neutral communication, chronological sorting, or timestamps.

Status of This Memo

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Copyright Notice

   Copyright (c) 2026 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Purpose . . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Design Principles . . . . . . . . . . . . . . . . . . . .   3
     1.3.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Conventions and Terminology . . . . . . . . . . . . . . . . .   4
   3.  Preferred Output  . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Canonical Form  . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Month . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.3.  Day . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.4.  Year  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.5.  Weekday . . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Syntax (ABNF) . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Permitted Yearless Variants . . . . . . . . . . . . . . . . .   7
     5.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.2.  Day-Month Variant Without Weekday Comma . . . . . . . . .   7
     5.3.  Month-Day Variant . . . . . . . . . . . . . . . . . . . .   8
     5.4.  Single-Digit Day in Informal Output . . . . . . . . . . .   8
   6.  Output Summary  . . . . . . . . . . . . . . . . . . . . . . .   8
   7.  Applicability . . . . . . . . . . . . . . . . . . . . . . . .   9
     7.1.  Recommended Uses  . . . . . . . . . . . . . . . . . . . .   9
     7.2.  Uses Requiring Another Format . . . . . . . . . . . . . .   9
   8.  Internationalization Considerations . . . . . . . . . . . . .   9
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     11.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  11
     A.1.  Canonical IMDF  . . . . . . . . . . . . . . . . . . . . .  11
     A.2.  Permitted Yearless Variants . . . . . . . . . . . . . . .  11
     A.3.  Not IMDF  . . . . . . . . . . . . . . . . . . . . . . . .  11
   Revision History  . . . . . . . . . . . . . . . . . . . . . . . .  12
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  12

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1.  Introduction

1.1.  Purpose

   All-numeric date formats can be misinterpreted when readers use
   different regional conventions.  For example:

   *  01/02/2026

   *  02/01/2026

   *  01.02.2026

   *  02-01-26

   Such forms do not visually identify which numeric field is the day
   and which is the month.  A reader may automatically apply a familiar
   ordering and fail to notice that the writer intended another one.

   Several established protocol specifications demonstrate the long-
   standing Internet practice of using alphabetic month abbreviations to
   eliminate date ambiguity.  These include ARPA Internet text messages
   (RFC 822 [RFC0822]), Internet Message Format (RFC 5322 [RFC5322]),
   and HTTP Semantics (RFC 9110 [RFC9110]).  However, those formats
   include protocol-heavy elements (timestamps, mandatory seconds, or
   time-zone offsets) optimized for machine parsing rather than concise
   human communication.

   IMDF addresses this problem by extracting that proven principle,
   using an English alphabetic month abbreviation, and applying it to a
   streamlined, presentation-only format for human-facing text:

   *  05 Jan 2026

   *  Jan 05

   *  Mon, 05 Jan 2026

   In each example, the alphabetic component unmistakably identifies the
   month.  The primary objective of IMDF is to reduce human
   interpretation errors in English-language date communication.

1.2.  Design Principles

   IMDF is guided by the following principles.

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   1.  *A month should never be mistaken for a day.*
       Every IMDF date contains an alphabetic month abbreviation.  The
       month is therefore visually distinct from the numeric day.

   2.  *Favor brevity.*
       IMDF uses three-letter month and weekday abbreviations so that
       dates remain practical in messages, comments, tickets, reports,
       presentations, and calendar annotations.

   3.  *Avoid number following number.*
       Alternating numeric and alphabetic components makes the date
       structure easier to recognize.  IMDF favors 05 Jan 2026 rather
       than an all-numeric sequence such as 05 01 2026.

   4.  *Respect established English-language conventions.*
       IMDF permits limited day-month and month-day variation when no
       year is shown.  This accommodates familiar English-language usage
       without making the month ambiguous.

   5.  *Prefer a unique canonical representation.*
       IMDF defines one preferred output form for consistent
       presentation.

1.3.  Scope

   IMDF represents a calendar date for human-readable English-language
   output.

   An IMDF date MAY include a year or MAY omit it.  When omitted, the
   year may be understood from context, supplied by surrounding text or
   metadata, intentionally irrelevant, or omitted because the date is
   recurring.  IMDF does not define how an omitted year is interpreted.

   IMDF does not represent an instant, time of day, duration, or time
   zone.

   ISO 8601 [ISO8601] SHOULD be used when language neutrality, machine
   interchange, chronological sorting, or non-English interoperability
   is required.

2.  Conventions and Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "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.

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   A "producer" is a person or implementation that presents an IMDF
   date.  "Canonical form" means the preferred output representation
   defined in Section 3.

3.  Preferred Output

3.1.  Canonical Form

   Producers SHOULD present IMDF dates in this canonical form:

   [ddd, ]DD MMM[ YYYY]

   where:

   *  ddd is an optional weekday abbreviation;

   *  DD is a two-digit day of the month;

   *  MMM is a three-letter month abbreviation; and

   *  YYYY is an optional four-digit year.

   Canonical examples:

   *  Mon, 05 Jan 2026

   *  05 Jan 2026

   *  Mon, 05 Jan

   *  05 Jan

3.2.  Month

   The month MUST be represented by one of these English abbreviations:

   Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

   The first letter SHOULD be uppercase and the remaining letters
   lowercase.

3.3.  Day

   In canonical output, the day MUST contain two decimal digits.  A
   leading zero MUST be used for days 1 through 9.

   Examples:

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   *  01 Jan

   *  05 Jan

   *  24 Aug

3.4.  Year

   When present, the year MUST contain four decimal digits and MUST
   follow the month.

   Examples:

   *  05 Jan 2026

   *  Mon, 24 Aug 2026

   Month-day-year output is not IMDF:

   *  Jan 05 2026

3.5.  Weekday

   A weekday MAY be included using one of these English abbreviations:

   Mon Tue Wed Thu Fri Sat Sun

   In canonical output, the weekday MUST precede the day and MUST be
   followed by a comma and one space.

   Examples:

   *  Mon, 05 Jan 2026

   *  Mon, 05 Jan

   The weekday SHOULD correspond to the represented calendar date when
   the year is known.

4.  Syntax (ABNF)

   The syntax of IMDF dates is specified using Augmented Backus-Naur
   Form (ABNF) as defined in [RFC5234].

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   imdf-date            = imdf-canonical / imdf-yearless

   ; Canonical Form
   imdf-canonical       = [ weekday ", " ] day " " month [ " " year ]

   ; Permitted Yearless Variants
   imdf-yearless        = imdf-day-first-var / imdf-month-first-var

   imdf-day-first-var   = [ weekday [ "," ] " " ] day-opt-zero " " month
   imdf-month-first-var = [ weekday ", " ] month " " day-opt-zero

   ; Core Elements
   day                  = 2DIGIT                  ; 01-31
   day-opt-zero         = 1*2DIGIT                ; 1-31 or 01-31

   month                = "Jan" / "Feb" / "Mar" / "Apr"
                        / "May" / "Jun" / "Jul" / "Aug"
                        / "Sep" / "Oct" / "Nov" / "Dec"

   weekday              = "Mon" / "Tue" / "Wed" / "Thu"
                        / "Fri" / "Sat" / "Sun"

   year                 = 4DIGIT                  ; 0000-9999

5.  Permitted Yearless Variants

5.1.  General

   A limited set of noncanonical variants MAY be used when the year is
   absent.  These variants reflect common English-language usage while
   retaining an alphabetic month.

   Producers SHOULD use the canonical form unless a permitted variant is
   more natural in the surrounding text.

5.2.  Day-Month Variant Without Weekday Comma

   In a yearless day-month date, the comma after a weekday MAY be
   omitted:

   *  Mon 05 Jan

   The canonical equivalent is:

   *  Mon, 05 Jan

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5.3.  Month-Day Variant

   When the year is absent, the month MAY precede the day:

   *  Jan 05

   If a weekday is included with month-day order, the weekday MUST be
   followed by a comma:

   *  Mon, Jan 05

   The following form is not IMDF:

   *  Mon Jan 05

5.4.  Single-Digit Day in Informal Output

   Informal output MAY omit the leading zero:

   *  5 Jan

   *  Jan 5

   *  Mon 5 Jan

   *  Mon, Jan 5

   Producers SHOULD use the two-digit day in canonical output.

6.  Output Summary

   Canonical output:

   [ddd, ]DD MMM[ YYYY]

   Additional permitted yearless output:

   [ddd ]D[D] MMM
   [ddd, ]MMM D[D]

   The following rules summarize IMDF output:

   1.  The month is always alphabetic.

   2.  A displayed year always follows the month.

   3.  Canonical output always places the day before the month.

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   4.  Canonical output always uses a two-digit day.

   5.  Canonical output uses a comma after a displayed weekday.

   6.  Month-day order is permitted only when the year is absent.

   7.  A weekday before a month-day date always requires a comma.

7.  Applicability

7.1.  Recommended Uses

   IMDF is intended for English-language human-facing content such as:

   *  messages and correspondence;

   *  comments and issue tickets;

   *  technical documentation and reports;

   *  presentations;

   *  calendar annotations; and

   *  short textual labels.

7.2.  Uses Requiring Another Format

   ISO 8601 SHOULD be preferred for:

   *  multilingual or language-neutral communication;

   *  machine interchange and software interfaces;

   *  database storage;

   *  chronological filename sorting; and

   *  applications requiring a standardized numeric date.

   A date-time format containing an offset or other time-zone
   information MUST be used when an absolute instant is required.

8.  Internationalization Considerations

   IMDF uses English ASCII weekday and month abbreviations.  Localized
   names are not IMDF.

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   IMDF SHOULD be used only where English-language date notation is
   expected and understood.  A localized format or ISO 8601 SHOULD be
   used in other language contexts.

9.  Security Considerations

   Ambiguous date interpretation can cause incorrect scheduling,
   retention, validity, or processing decisions.  IMDF reduces this risk
   by making the month alphabetic and visually distinct from the numeric
   day.

   A yearless IMDF date does not identify a unique calendar year.  A
   specific year MUST NOT be assumed unless it is provided by context
   outside IMDF.

   IMDF contains neither a time of day nor a time zone.  It MUST NOT be
   used to represent an absolute instant.

10.  IANA Considerations

   This document has no IANA actions.

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

11.2.  Informative References

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC0822]  Crocker, D., "STANDARD FOR THE FORMAT OF ARPA INTERNET
              TEXT MESSAGES", STD 11, RFC 822, DOI 10.17487/RFC822,
              August 1982, <https://www.rfc-editor.org/info/rfc822>.

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   [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
              DOI 10.17487/RFC5322, October 2008,
              <https://www.rfc-editor.org/info/rfc5322>.

   [RFC9110]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "HTTP Semantics", STD 97, RFC 9110,
              DOI 10.17487/RFC9110, June 2022,
              <https://www.rfc-editor.org/info/rfc9110>.

   [ISO8601]  International Organization for Standardization, "Date and
              time - Representations for information interchange - Part
              1: Basic rules", ISO 8601-1:2019, February 2019.

Appendix A.  Examples

A.1.  Canonical IMDF

   *  Mon, 05 Jan 2026

   *  05 Jan 2026

   *  Mon, 05 Jan

   *  05 Jan

A.2.  Permitted Yearless Variants

   *  Mon 05 Jan

   *  Jan 05

   *  Mon, Jan 05

   *  5 Jan

   *  Jan 5

   *  Mon 5 Jan

   *  Mon, Jan 5

A.3.  Not IMDF

   *  24 August 2026 - Full month names are not defined.

   *  24-AUG-2026 - Hyphens are not defined.

   *  2026 Aug 24 - Year-first order is not defined.

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   *  Jan 05 2026 - Month-day order cannot include a year.

   *  Mon 24 Aug 2026 - A weekday before a dated year needs comma.

   *  Mon Jan 05 - Month-day order requires a weekday comma.

   *  24/08/2026 - The month is numeric.

   *  2026-08-24 - This is ISO 8601, not IMDF.

Revision History

Author's Address

   Thomas Henlich
   Henlich Engineering
   Gruenewaldstr. 57
   74080 Heilbronn
   Germany
   Email: thomas@henlich.de
   URI:   https://henlich.de/

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