text/markdown Use Cases
draft-ietf-appsawg-text-markdown-use-cases-00

Applications Area Working Group                               S. Leonard
Internet-Draft                                             Penango, Inc.
Intended Status: Informational                         February 21, 2015
Expires: August 25, 2015                                                

                        text/markdown Use Cases
             draft-ietf-appsawg-text-markdown-use-cases-00

Abstract

   This document elaborates upon the text/markdown media type for use
   with Markdown, a family of plain text formatting syntaxes that
   optionally can be converted to formal markup languages such as HTML.
   Background information, local storage strategies, and additional
   syntax registrations are supplied.

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

Copyright Notice

   Copyright (c) 2015 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
   (http://trustee.ietf.org/license-info) 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
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

 

Leonard                   Exp. August 25, 2015                  [Page 1]
Internet-Draft          text/markdown Use Cases            February 2015

Table of Contents

   1.  Dive Into Markdown . . . . . . . . . . . . . . . . . . . . . .  2
     1.1. On Formats  . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.2. Markdown Design Philosophy  . . . . . . . . . . . . . . . .  4
     1.3. Uses of Markdown  . . . . . . . . . . . . . . . . . . . . .  5
     1.4. Uses of Labeling Markdown Content as text/markdown  . . . .  5
   2.  Strategies for Preserving Media Type and Parameters  . . . . .  6
     2.1. Map to Filename and Attributes  . . . . . . . . . . . . . .  7
     2.2. Store Headers in Adjacent File  . . . . . . . . . . . . . .  8
     2.3. "Arm" Content with MIME Headers . . . . . . . . . . . . . .  8
     2.4. Create a Local Batch Script . . . . . . . . . . . . . . . .  8
     2.5. Process the Markdown  . . . . . . . . . . . . . . . . . . .  8
     2.6. Rely on Context . . . . . . . . . . . . . . . . . . . . . .  8
     2.7. Specific Strategies . . . . . . . . . . . . . . . . . . . .  9
       2.7.1. Subversion  . . . . . . . . . . . . . . . . . . . . . .  9
       2.7.2. Git . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   3.  Registration Templates for Common Markdown Syntaxes  . . . . . 10
     3.1. MultiMarkdown . . . . . . . . . . . . . . . . . . . . . . . 10
     3.2. GitHub Flavored Markdown  . . . . . . . . . . . . . . . . . 11
     3.3. Pandoc  . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     3.4. Fountain (Fountain.io)  . . . . . . . . . . . . . . . . . . 13
     3.5. CommonMark  . . . . . . . . . . . . . . . . . . . . . . . . 14
     3.6. kramdown-rfc2629 (Markdown for RFCs)  . . . . . . . . . . . 15
     3.7. rfc7328 (Pandoc2rfc)  . . . . . . . . . . . . . . . . . . . 15
     3.8. PHP Markdown Extra  . . . . . . . . . . . . . . . . . . . . 15
   4.  Examples for Common Markdown Syntaxes  . . . . . . . . . . . . 16
     4.1. MultiMarkdown . . . . . . . . . . . . . . . . . . . . . . . 16
     4.2. GitHub Flavored Markdown  . . . . . . . . . . . . . . . . . 16
     4.3. Pandoc  . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     4.4. Fountain (Fountain.io)  . . . . . . . . . . . . . . . . . . 16
     4.5. CommonMark  . . . . . . . . . . . . . . . . . . . . . . . . 16
     4.6. kramdown-rfc2629 (Markdown for RFCs)  . . . . . . . . . . . 16
     4.7. rfc7328 (Pandoc2rfc)  . . . . . . . . . . . . . . . . . . . 16
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   6. Security Considerations . . . . . . . . . . . . . . . . . . . . 16
   7. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     7.1. Normative References  . . . . . . . . . . . . . . . . . . . 16
     7.2. Informative References  . . . . . . . . . . . . . . . . . . 17
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 18

1.  Dive Into Markdown

   This document serves as an informational companion to [MDMTREG], the
   text/markdown media type registration. It should be considered
   jointly with [MDMTREG].

 

Leonard                   Exp. August 25, 2015                  [Page 2]
Internet-Draft          text/markdown Use Cases            February 2015

         "Sometimes the truth of a thing is not so much in the
         think of it, but in the feel of it." --Stanley Kubrick

1.1. On Formats

   In computer systems, textual data is stored and processed using a
   continuum of techniques. On the one end is plain text: a linear 
   sequence of characters in some character set (code), possibly
   interrupted by line breaks, page breaks, or other control characters.
   Plain text provides /some/ fixed facilities for formatting
   instructions, namely codes in the character set that have meanings
   other than "represent this character on the output medium"; however,
   these facilities are not particularly extensible. Compare with
   [RFC6838] Section 4.2.1. Applications may neuter the effects of these
   special characters by prohibiting them or by ignoring their dictated
   meanings, as is the case with how modern applications treat most
   control characters in US-ASCII. On this end, any text reader or
   editor that interprets the character set can be used to see or
   manipulate the text. If some characters are corrupted, the corruption
   is unlikely to affect the ability of a computer system to process the
   text (even if the human meaning is changed).

   On the other end is binary format: a sequence of instructions
   intended for some computer application to interpret and act upon.
   Binary formats are flexible in that they can store non-textual data
   efficiently (perhaps storing no text at all, or only storing certain
   kinds of text for very specialized purposes). Binary formats require
   an application to be coded specifically to handle the format; no
   partial interoperability is possible. Furthermore, if even one byte
   or bit are corrupted in a binary format, it may prevent an
   application from processing any of the data correctly.

   Between these two extremes lies formatted text, i.e., text that
   includes non-textual information coded in a particular way, that
   affects the interpretation of the text by computer programs.
   Formatted text is distinct from plain text and binary format in that
   the non-textual information is encoded into textual characters, which
   are assigned specialized meanings /not/ defined by the character set.
   With a regular text editor and a standard keyboard (or other standard
   input mechanism), a user can enter these textual characters to
   express the non-textual meanings. For example, a character like "<"
   no longer means "LESS-THAN SIGN"; it means the start of a tag or
   element that affects the document in some way.

   On the formal end of the spectrum is markup, a family of languages
   for annotating a document in such a way that the annotations are
   syntactically distinguishable from the text. Markup languages are
   (reasonably) well-specified and tend to follow (mostly) standardized
 

Leonard                   Exp. August 25, 2015                  [Page 3]
Internet-Draft          text/markdown Use Cases            February 2015

   syntax rules. Examples of markup languages include SGML, HTML, XML,
   and LaTeX. Standardized rules lead to interoperability between markup
   processors, but a skill requirement for new (human) users of the
   language that they learn these rules in order to do useful work. This
   imposition makes markup less accessible for non-technical users
   (i.e., users who are unwilling or unable to invest in the requisite
   skill development).

     informal        /---------formatted text----------\        formal
     <------v-------------v-------------v-----------------------v---->
      plain text     informal markup   formal markup    binary format
                     (Markdown)        (HTML, XML, etc.)

    Figure 1: Degrees of Formality in Data Storage Formats for Text

   On the informal end of the spectrum are lightweight markup languages.
   In comparison with formal markup like XML, lightweight markup uses
   simple syntax, and is designed to be easy for humans to enter with
   basic text editors. Markdown, the subject of this document, is an
   /informal/ plain text formatting syntax that is intentionally
   targeted at non-technical users (i.e., users upon whom little to no
   skill development is imposed) using unspecialized tools (i.e., text
   boxes). Jeff Atwood once described these informal markup languages as
   "humane" [HUMANE].

1.2. Markdown Design Philosophy

   Markdown specifically is a family of syntaxes that are based on the
   original work of John Gruber with substantial contributions from
   Aaron Swartz, released in 2004 [MARKDOWN]. Since its release a number
   of web or web-facing applications have incorporated Markdown into
   their text entry systems, frequently with custom extensions. Fed up
   with the complexity and security pitfalls of formal markup languages
   (e.g., HTML5) and proprietary binary formats (e.g., commercial word
   processing software), yet unwilling to be confined to the
   restrictions of plain text, many users have turned to Markdown for
   document processing. Whole toolchains now exist to support Markdown
   for online and offline projects.

   Informality is a bedrock premise of Gruber's design. Gruber created
   Markdown after disastrous experiences with strict XML and XHTML
   processing of syndicated feeds. In Mark Pilgrim's "thought
   experiment", several websites went down because one site included
   invalid XHTML in a blog post, which was automatically copied via
   trackbacks across other sites [DIN2MD]. These scenarios led Gruber to
   believe that clients (e.g., web browsers) SHOULD try to make sense of
   data that they receive, rather than rejecting data simply because it
   fails to adhere to strict, unforgiving standards. (In [DIN2MD],
 

Leonard                   Exp. August 25, 2015                  [Page 4]
Internet-Draft          text/markdown Use Cases            February 2015

   Gruber compared Postel's Law [RFC0793] with the XML standard, which
   says: "Once a fatal error is detected [...] the processor MUST NOT
   continue normal processing" [XML1.0-5].) As a result, there is no
   such thing as "invalid" Markdown; there is no standard demanding
   adherence to the Markdown syntax; there is no governing body that
   guides or impedes its development. If the Markdown syntax does not
   result in the "right" output (defined as output that the author
   wants, not output that adheres to some dictated system of rules),
   Gruber's view is that the author either should keep on experimenting,
   or should change the processor to address the author's particular
   needs (see [MARKDOWN] Readme and [MD102b8] perldoc; see also
   [CATPICS]).

1.3. Uses of Markdown

   Since its introduction in 2004, Markdown has enjoyed remarkable
   success. Markdown works for users for three key reasons. First, the
   markup instructions (in text) look similar to the markup that they
   represent; therefore the cognitive burden to learn the syntax is low.
   Second, the primary arbiter of the syntax's success is *running
   code*. The tool that converts the Markdown to a presentable format,
   and not a series of formal pronouncements by a standards body, is the
   basis for whether syntactic elements matter. Third, Markdown has
   become something of an Internet meme [INETMEME], in that Markdown
   gets received, reinterpreted, and reworked as additional communities
   encounter it. There are communities that are using Markdown for
   scholarly writing [CITE], for screenplays [FOUNTAIN], for
   mathematical formulae [CITE], and even for music annotation [CITE].
   Clearly, a screenwriter has no use for specialized Markdown syntax
   for mathematicians; likewise, mathematicians do not need to identify
   characters or props in common ways. The overall gist is that all of
   these communities can take the common elements of Markdown (which are
   rooted in the common elements of HTML circa 2004) and build on them
   in ways that best fit their needs.

1.4. Uses of Labeling Markdown Content as text/markdown

   The primary purpose of an Internet media type is to label "content"
   on the Internet, as distinct from "files". Content is any computer-
   readable format that can be represented as a primary sequence of
   octets, along with type-specific metadata (parameters) and type-
   agnostic metadata (protocol dependent). From this description, it is
   apparent that appending ".markdown" to the end of a filename is not a
   sufficient means to identify Markdown. Filenames are properties of
   files in file systems, but Markdown frequently exists in databases or
   content management systems (CMSes) where the file metaphor does not
   apply. One CMS [RAILFROG] uses media types to select appropriate
   processing, so a media type is necessary for the safe and
 

Leonard                   Exp. August 25, 2015                  [Page 5]
Internet-Draft          text/markdown Use Cases            February 2015

   interoperable use of Markdown.

   Unlike complete HTML documents, [MDSYNTAX] provides no means to
   include metadata into the content stream. Several derivative flavors
   have invented metadata incorporation schemes (e.g., [MULTIMD]), but
   these schemes only address specific use cases. In general, the
   metadata must be supplied via supplementary means in an encapsulating
   protocol, format, or convention. The relationship between the content
   and the metadata is not directly addressed here or in [MDMTREG];
   however, by identifying Markdown with a media type, Markdown content
   can participate as a first-class citizen with a wide spectrum of
   metadata schemes.

   Finally, registering a media type through the IETF process is not
   trivial. Markdown can no longer be considered a "vendor"-specific
   innovation, but the registration requirements even in the vendor tree
   have proven to be overly burdensome for most Markdown implementers.
   Moreover, registering hundreds of Markdown variants with distinct
   media types would impede interoperability: virtually all Markdown
   content can be processed by virtually any Markdown processor, with
   varying degrees of success. The goal of [MDMTREG] is to reduce all of
   these burdens by having one media type that accommodates diversity
   and eases registration.

2.  Strategies for Preserving Media Type and Parameters

   The purpose of this document and [MDMTREG] is to promote
   interoperability between different Markdown-related systems,
   preserving the author's intent. While [MARKDOWN] was designed by
   Gruber in 2004 as a simple way to write blog posts and comments, as
   of 2014 Markdown and its derivatives are rapidly becoming the formats
   of record for many communities and use cases. While an individual
   member of (or software tool for) a community can probably look at
   some "Markdown" and declare its meaning intuitively obvious, software
   systems in different communities (or different times) need help.
   [MDSYNTAX] does not have a signaling mechanism like <!DOCTYPE>, so
   tagging Markdown internally is simply out of the question. Once tags
   or metadata are introduced, the content is no longer "just" Markdown.

   Some commentators have suggested that an in-band signaling mechanism,
   such as in Markdown link definitions at the top of the content, could
   be used to signal the variant. Unfortunately this signaling mechanism
   is incompatible with other Markdown variants (e.g., [PANDOC]) that
   expect their own kinds of metadata at the top of the file. Markdown
   content is just a stream of text; the semantics of that text can only
   be furnished by context.

   The media type and variant parameter in [MDMTREG] furnish this
 

Leonard                   Exp. August 25, 2015                  [Page 6]
Internet-Draft          text/markdown Use Cases            February 2015

   missing context, while allowing for additional extensibility. This
   section covers strategies for how an application might preserve
   metadata when it leaves the domain of IETF protocols.

   [MDMTREG] (draft-05) only defines two parameters: the charset
   parameter (required for all text/* media types) and the variant
   parameter. Character set interoperability is well-studied territory
   [NB: CITE?] and so is not further covered here. The variant parameter
   provides a simple identifier--nothing less or more. Variants are
   allowed to define additional parameters when sent with the
   text/markdown media type; the variant can also introduce control
   information into the textual content stream (such as via a metadata
   block). Neither [MDMTREG] nor this specification recommend any
   particular approach. However, the philosophy behind [MDMTREG] is to
   preserve formats rather than create new ones, since supporting
   existing toolchains is more realistic than creating novel ones that
   lack traction in the Markdown community.

2.1. Map to Filename and Attributes

   This strategy is to map the media type, variant, and parameters to
   "attributes" or "forks" in the local convention. Firstly, Markdown
   content saved to a file should have an appropriate file extension
   ending in .md or .markdown, which serves to disambiguate it from
   other kinds of files. The character repertoire of variant identifiers
   in [MDMTREG] is designed to be compatible with most filename
   conventions. Therefore, a recommended strategy is to record the
   variant identifier as the prefix to the file extension. For example,
   for [PANDOC] content, a file could be named
   "example.pandoc.markdown".

   Many filesystems are case-sensitive or case-preserving; however, file
   extensions tend to be all-lowercase. This document takes no position
   on whether variant identifiers should be case-preserved or all-
   lowercase when Markdown content is written to a file. However, when
   the variant identifier is read to influence operational behavior, it
   needs to be compared case-insensitively.

   Many modern filesystems support "extended attributes", "alternate
   data streams", or "resource forks". Some version control systems
   support named properties. If the variant defines additional
   parameters, these parameters should be stored in these resources,
   where the parameter name includes the name of the resource, and the
   parameter value is the value of the resource (data in the resource),
   preferably UTF-8 encoded (unless the parameter definition explicitly
   defines a different encoding or repertoire). The variant identifier
   itself should be stored in a resource with a name including the term
   "variant".
 

Leonard                   Exp. August 25, 2015                  [Page 7]
Internet-Draft          text/markdown Use Cases            February 2015

2.2. Store Headers in Adjacent File

   This strategy is to save the Markdown content in a first file, and to
   save the metadata (specifically the Content-Type: header) in a second
   file with a filename that is rationally related to the first
   filename. For example, if the first file is named "readme.markdown",
   the second file could be named "readme.markdown.headers". (If stored
   in a database, the analogy would be to store the metadata in a second
   table with a field that is a key to the first table.) This header
   file has the media type "message/global-headers" [RFC6533] (".u8hdr"
   suggestion notwithstanding).

2.3. "Arm" Content with MIME Headers

   This strategy is to save the Markdown content along with its headers
   in a file, "arming" the content by prepending the MIME headers
   (specifically the Content-Type: header). It should be appreciated
   that the file is no longer a "Markdown file"; rather, it is an
   Internet Message Format file (e.g., [RFC5322]) with a Markdown
   content part. Therefore, the file should have an Internet message
   extension (e.g., ".eml", ".msg", or ".u8msg"), not a Markdown
   extension (e.g., ".md" or ".markdown").

2.4. Create a Local Batch Script

   This strategy is to translate the processing instructions inferred
   from the Content-Type and other parameters (e.g., Content-
   Disposition) into a sequence of commands in the local convention,
   storing those commands in a batch script. For example, when a MIME-
   aware client stores some Markdown to disk, the client can save a
   Makefile in the same directory with commands that are appropriate
   (and safe) for the local system.

2.5. Process the Markdown

   This strategy is to process the Markdown into the formal markup,
   which eliminates ambiguities. Once the Markdown is processed into
   (for example) valid XHTML, an application can save a file as
   "doc.xhtml" with no further loss of metadata. While unambiguous, this
   process may not be reversible.

2.6. Rely on Context

   This last strategy is to use or create context to determine how to
   interpret the Markdown. For example, Markdown content that is of the
   Fountain.io type [FOUNTAIN] could be saved with the filename
   "script.fountain" instead of "script.markdown". Alternatively,
   scripts could be stored in a "/screenplays" directory while other
 

Leonard                   Exp. August 25, 2015                  [Page 8]
Internet-Draft          text/markdown Use Cases            February 2015

   kinds of Markdown could be stored elsewhere. For reasons that should
   be intuitively obvious, this method is the most error-prone.
   "Context" can be easily lost over time, and the trend of passing
   Markdown between systems--taking them *out* of context--is
   increasing.

2.7. Specific Strategies

2.7.1. Subversion

   This subsection covers a preservation strategy in Subversion [SVN], a
   common client-server version control system.

   Subversion supports named properties. The "svn:mime-type" property
   duplicates the entire Content-Type header, so parameters SHOULD be
   stored there. The filename SHOULD be consistent with this Content-
   Type header, i.e., the extension SHOULD be the variant identifier
   plus ".markdown".

   [[TODO: Versions of Subversion after [[1.x]] treat svn:mime-type as
   UTF-8 encoded, rather than US-ASCII. (See [RFC6532].) Therefore, the
   encoding of [RFC2231] will not be necessary in the vast majority of
   cases in newer versions. However, both for backwards compatibility
   and for support for non-Unicode character sets, [RFC2231] still needs
   to be supported.]]

   [[TODO: Where to store Content-Disposition?]]

2.7.2. Git

   This subsection covers a preservation strategy in Git [GIT], a common
   distributed version control system.

   Versions of Git as of the time of this writing do not support
   arbitrary metadata storage; however, third-party projects add this
   support.

   If Git is used without a metadata storage service, then a reasonable
   strategy is to include the variant identifier in the filename. The
   encoding of the file should be transcoded to UTF-8. For other
   properties, a header file should be recorded alongside the Markdown
   file in accordance with Section 2.2. The contents of the header file
   should be consistent with the rest of this paragraph, i.e., the
   charset parameter should be "UTF-8" and the variant parameter should
   match the identifier in the filename.

   If a metadata storage service is used with Git, then use a convention
   that is most analogous to the service. For example, the "metastore"
 

Leonard                   Exp. August 25, 2015                  [Page 9]
Internet-Draft          text/markdown Use Cases            February 2015

   project emulates extended attributes (xattrs) of a POSIX-like system,
   so whatever "xattr" methodology is developed would be usable with
   metastore and Git.

3.  Registration Templates for Common Markdown Syntaxes

   The purpose of this section is to register certain syntaxes in the
   Markdown Syntaxes Registry [MDMTREG] because they illustrate
   particularly interesting use cases or are broadly applicable to the
   Internet community; thus, these syntaxes would benefit from the level
   of review associated with publication as IETF documents.

3.1. MultiMarkdown

   Identifier: MultiMarkdown

   Name: MultiMarkdown

   Description:
   MultiMarkdown (MMD) is a superset of "Original". It adds multiple
   syntax features (tables, footnotes, and citations, to name a few),
   and is intended to output to various formats. Additionally, it builds
   in "smart" typography for various languages (proper left- and right-
   sided quotes, for example).

   Additional Parameters:
    options: String with zero or more of the following WSP-delimited
             tokens:

                "memoir" / "beamer"
                "full" / "snippet"
                "process-html"
                "random-footnote-identifiers"
                "accept"
                "reject"
                "nosmart"
                "nonotes"
                "nolabels"
                "nomask"

             The meanings of these tokens are defined in the
             MultiMarkdown documentation.

   References:
   <http://fletcher.github.io/MultiMarkdown-4/syntax>

   Contact Information:
     (individual) Fletcher T. Penney <fletcher@fletcherpenney.net>
 

Leonard                   Exp. August 25, 2015                 [Page 10]
Internet-Draft          text/markdown Use Cases            February 2015

                        <http://fletcherpenney.net/multimarkdown/>

3.2. GitHub Flavored Markdown

   Identifier: GFM

   Name: GitHub Flavored Markdown

   Description:
   "Original" with the following differences:
      1. Multiple underscores in words
      2. URL (URI) autolinking
      3. Strikethrough
      4. Fenced code blocks
      5. Syntax highlighting
      6. Tables (- for rows; | for columns; : for alignment)
      7. Only some HTML allowed; sanitization is integral
         to the format

   References:
   <https://help.github.com/articles/github-flavored-markdown/>
   <https://github.com/github/markup/tree/master#html-sanitization>

   Contact Information:
     (corporate) GitHub, Inc. <https://github.com/contact>
               [[Vicent Marti <vicent@github.com>??]]

3.3. Pandoc

   Identifier: pandoc

   Name: Pandoc

   Description:
   Markdown is designed to be easy to write and to read: the content
   should be publishable as-is, as plain text, without looking like it
   has been marked up with tags or formatting instructions. Yet whereas
   "Original" has HTML generation in mind, pandoc is designed for
   multiple output formats. Thus, while pandoc allows the embedding of
   raw HTML, it discourages it, and provides other, non-HTMLish ways of
   representing important document elements like definition lists,
   tables, mathematics, and footnotes.

   Additional Parameters:
    extensions: String with an optional starting syntax token, followed
                by a "+" and "-" delimited list of extension tokens. "+"
                preceding an extension token turns the extension on; "-"
                turns the extension off.  The starting syntax tokens are
 

Leonard                   Exp. August 25, 2015                 [Page 11]
Internet-Draft          text/markdown Use Cases            February 2015

                "markdown", "markdown_strict", "markdown_phpextra", and
                "markdown_github". If no starting syntax token is given,
                "markdown" is assumed. The extension tokens include:

                   [[Stuff to turn off:]]

                   escaped_line_breaks
                   blank_before_header
                   header_attributes
                   auto_identifiers
                   implicit_header_references
                   blank_before_blockquote
                   fenced_code_blocks
                   fenced_code_attributes
                   line_blocks
                   fancy_lists
                   startnum
                   definition_lists
                   example_lists
                   table_captions
                   simple_tables
                   multiline_tables
                   grid_tables
                   pipe_tables
                   pandoc_title_block
                   yaml_metadata_block
                   all_symbols_escapable
                   intraword_underscores
                   strikeout
                   superscript
                   subscript
                   inline_code_attributes
                   tex_math_dollars
                   raw_html
                   markdown_in_html_blocks
                   native_divs
                   native_spans
                   raw_tex
                   latex_macros
                   implicit_figures
                   footnotes
                   inline_notes
                   citations

                   [[New stuff:]]

                   lists_without_preceding_blankline
                   hard_line_breaks
 

Leonard                   Exp. August 25, 2015                 [Page 12]
Internet-Draft          text/markdown Use Cases            February 2015

                   ignore_line_breaks
                   tex_math_single_backslash
                   tex_match_double_backslash
                   markdown_attribute
                   mmd_title_block
                   abbreviations
                   autolink_bare_uris
                   ascii_identifiers
                   link_attributes
                   mmd_header_identifiers
                   compact_definition_lists

   Fragment Identifiers:
   Pandoc defines fragment identifiers using the <id> in the
   {#<id> .class ...} production (PHP Markdown Extra attribute block).
   This syntax works for Header Identifiers and Code Block Identifiers.

   References:
   <http://johnmacfarlane.net/pandoc/README.html#pandocs-markdown>

   Contact Information:
     (individual) Prof. John MacFarlane <jgm@berkeley.edu>
                              <http://johnmacfarlane.net/>

3.4. Fountain (Fountain.io)

   Identifier: Fountain

   Name: Fountain

   Description:
   Fountain is a simple markup syntax for writing, editing and sharing
   screenplays in plain, human-readable text. Fountain allows you to
   work on your screenplay anywhere, on any computer or tablet, using
   any software that edits text files.

   Fragment Identifiers:
   See <http://fountain.io/syntax#section-titlepage> and
   <http://fountain.io/syntax#section-sections>. In the following
   fragment identifiers, the <key> and <sec*> productions MUST have "/"
   characters percent-encoded.

   #/       Title Page (acts as metadata).
   #/<key>  Title Page; <key> is the key string.
   #<sec1> *("/" <secn>)
            Section or subsection. The <sec1>..<secn>
            productions are the text of the Section line,
            with whitespace trimmed from both ends.
 

Leonard                   Exp. August 25, 2015                 [Page 13]
Internet-Draft          text/markdown Use Cases            February 2015

            Sub-sections (sections with multiple # at
            at the beginning of the line in the source)
            are addressed hierarchically by preceding
            the sub-section with higher-order
            sections. If the section hierarchy "skips",
            e.g., # to ###, use a blank section name,
            e.g., #Section/ACT%20I//PATIO%20SCENE.

   References:
   <http://fountain.io/syntax>

   Contact Information:
     (individual) Stu Maschwitz <http://prolost.com/>
     (individual) John August <http://johnaugust.com/>

3.5. CommonMark

   Identifier: CommonMark

   Name: CommonMark

   Description:
   CommonMark is a standard, unambiguous syntax specification for
   Markdown, along with a suite of comprehensive tests to validate
   Markdown implementations against this specification. The maintainers
   believe that CommonMark is necessary, even essential, for the future
   of Markdown.

   Compared to "Original", CommonMark is much longer and in a few
   instances contradicts "Original" based on seasoned experience.
   Although CommonMark specifically does not mandate any particular
   encoding for the input content, CommonMark draws in more of Unicode,
   UTF-8, and HTML (including HTML5) than "Original".

   This registration always refers to the latest version or an
   unspecified version (receiver's choice). Version 0.13 of the
   CommonMark specification was released 2014-12-10.

   References:
   <http://spec.commonmark.org/>

   Contact Information:
     (individual) John MacFarlane <jgm@berkeley.edu>
     (individual) David Greenspan <david@meteor.com>
     (individual) Vicent Marti <vicent@github.com>
     (individual) Neil Williams <neil@reddit.com>
     (individual) Benjamin Dumke-von der Ehe <ben@stackexchange.com>
     (individual) Jeff Atwood <jatwood@codinghorror.com>
 

Leonard                   Exp. August 25, 2015                 [Page 14]
Internet-Draft          text/markdown Use Cases            February 2015

3.6. kramdown-rfc2629 (Markdown for RFCs)

   Identifier: kramdown-rfc2629

   Name: Markdown for RFCs

   Description:
   kramdown is a markdown parser by Thomas Leitner, which has a number
   of backends for generating HTML, Latex, and Markdown again. kramdown-
   rfc2629 is an additional backend to that: It allows the generation of
   XML2RFC XML markup (also known as RFC 2629 compliant markup).

   References:
   <https://github.com/cabo/kramdown-rfc2629>

   Contact Information:
     (individual) Carsten Bormann <cabo@tzi.org>

3.7. rfc7328 (Pandoc2rfc)

   Identifier: rfc7328

   Name: Pandoc2rfc

   Description:
   Pandoc2rfc allows authors to write in "pandoc" that is then
   transformed to XML and given to xml2rfc.  The conversions are, in a
   way, amusing, as we start off with (almost) plain text, use elaborate
   XML, and end up with plain text again.

   References:
   RFC 7328
   <https://github.com/miekg/pandoc2rfc>

   Contact Information:
     (individual) R. (Miek) Gieben <miek@google.com>

3.8. PHP Markdown Extra

   Identifier: Extra

   Name: Markdown Extra

   Description:
   Markdown Extra is an extension to PHP Markdown implementing some
   features currently not available with the plain Markdown syntax.
   Markdown Extra is available as a separate parser class in PHP
   Markdown Lib. Other implementations include Maruku (Ruby) and Python
 

Leonard                   Exp. August 25, 2015                 [Page 15]
Internet-Draft          text/markdown Use Cases            February 2015

   Markdown. Markdown Extra is supported in several content management
   systems, including Drupal, TYPO3, and MediaWiki.

   Fragment Identifiers:
   Markdown Extra defines fragment identifiers using the <id> in the
   {#<id> .class ...} production (attribute block). This syntax works
   for headers, fenced code blocks, links, and images.

   References:
   <https://michelf.ca/projects/php-markdown/extra/>

   Contact Information:
     (individual) Michel Fortin <michel.fortin@michelf.ca>

4.  Examples for Common Markdown Syntaxes

   This section provides examples of the variants registered in Appendix
   C.

4.1. MultiMarkdown

4.2. GitHub Flavored Markdown

4.3. Pandoc

4.4. Fountain (Fountain.io)

4.5. CommonMark

4.6. kramdown-rfc2629 (Markdown for RFCs)

4.7. rfc7328 (Pandoc2rfc)

   [[TODO: complete.]]

5.  IANA Considerations

   IANA is asked to register the syntaxes specified in Section 3 in the
   Markdown Variants Registry.

6. Security Considerations

   See the respective syntax descriptions and output media type
   registrations for their respective security considerations.

7. References

7.1. Normative References
 

Leonard                   Exp. August 25, 2015                 [Page 16]
Internet-Draft          text/markdown Use Cases            February 2015

   [MARKDOWN] Gruber, J., "Daring Fireball: Markdown", December 2004,
              <http://daringfireball.net/projects/markdown/>.

   [MDSYNTAX] Gruber, J., "Daring Fireball: Markdown Syntax
              Documentation", December 2004,
              <http://daringfireball.net/projects/markdown/syntax>.

   [MDMTREG]  Leonard, S., "The text/markdown Media Type", draft-ietf-
              appsawg-text-markdown-05 (work in progress), December
              2014.

   [RFC5147]  Wilde, E. and M. Duerst, "URI Fragment Identifiers for the
              text/plain Media Type", RFC 5147, April 2008.

   [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
              October 2008.

7.2. Informative References

   [HUMANE]   Atwood, J., "Is HTML a Humane Markup Language?", May 2008,
              <http://blog.codinghorror.com/is-html-a-humane-markup-
              language/>.

   [DIN2MD]   Gruber, J., "Dive Into Markdown", March 2004,
              <http://daringfireball.net/2004/03/dive_into_markdown>.

   [MD102b8]  Gruber, J., "[ANN] Markdown.pl 1.0.2b8", May 2007,
              <http://six.pairlist.net/pipermail/markdown-discuss/2007-
              May/000615.html>, <http://daringfireball.net/projects/
              downloads/Markdown_1.0.2b8.tbz>.

   [CATPICS]  Gruber, J. and M. Arment, "The Talk Show: Ep. 88: 'Cat
              Pictures' (Side 1)", July 2014,
              <http://daringfireball.net/thetalkshow/2014/07/19/ep-088>.

   [INETMEME] Solon, O., "Richard Dawkins on the internet's hijacking of
              the word 'meme'", June 2013,
              <http://www.wired.co.uk/news/archive/2013-06/20/richard-
              dawkins-memes>, <http://www.webcitation.org/6HzDGE9Go>.

   [MULTIMD]  Penney, F., "MultiMarkdown", April 2014,
              <http://fletcherpenney.net/multimarkdown/>.

   [PANDOC]   MacFarlane, J., "Pandoc", 2014,
              <http://johnmacfarlane.net/pandoc/>.

   [RAILFROG] Railfrog Team, "Railfrog", April 2009,
              <http://railfrog.com/>.
 

Leonard                   Exp. August 25, 2015                 [Page 17]
Internet-Draft          text/markdown Use Cases            February 2015

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7, RFC
              793, September 1981.

   [RFC2231]  Freed, N. and K. Moore, "MIME Parameter Value and Encoded
              Word Extensions: Character Sets, Languages, and
              Continuations", RFC 2231, November 1997.

   [RFC4263]  Lilly, B., "Media Subtype Registration for Media Type
              text/troff", RFC 4263, January 2006.

   [RFC6533]  Hansen, T., Ed., Newman, C. and A. Melnikov,
              "Internationalized Delivery Status and Disposition
              Notifications", RFC 6533, February 2012.

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13, RFC
              6838, January 2013.

   [XML1.0-5] Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and
              F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth
              Edition)", World Wide Web Consortium Recommendation REC-
              xml-20081126, November 2008,
              <http://www.w3.org/TR/2008/REC-xml-20081126#dt-fatal>.

   [FOUNTAIN] Maschwitz, S. and J. August, "Fountain | A markup language
              for screenwriting.", 2014, <http://fountain.io/>.

   [FTSYNTAX] Maschwitz, S. and J. August, "Syntax - Fountain | A markup
              language for screenwriting.", 1.1, March 2014,
              <http://fountain.io/syntax>.

   [SVN]      Apache Subversion, December 2014,
              <https://subversion.apache.org/>.

   [GIT]      Git, December 2014, <http://git-scm.com/>.

Author's Address

   Sean Leonard
   Penango, Inc.
   5900 Wilshire Boulevard
   21st Floor
   Los Angeles, CA  90036
   USA

   EMail: dev+ietf@seantek.com
   URI:   http://www.penango.com/

Leonard                   Exp. August 25, 2015                 [Page 18]