xeps/inbox/styling.xml

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<!DOCTYPE xep SYSTEM 'xep.dtd' [
  <!ENTITY % ents SYSTEM 'xep.ent'>
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<!ENTITY rfc7764 "<span class='ref'><link url='http://tools.ietf.org/html/rfc7764'>RFC 7764</link></span> <note>RFC 7764: Guidance on Markdown: Design Philosophies, Stability Strategies, and Select Registrations &lt;<link url='http://tools.ietf.org/html/rfc7764'>http://tools.ietf.org/html/rfc7764</link>&gt;.</note>" >
<!ENTITY uax9 "<span class='ref'>Unicode Standard Annex #9</span> <note>Unicode Standard Annex #9, &quot;Unicode Bidirectional Algorithm&quot;, edited by Mark Davis, Aharon Lanin, and Andrew Glass. An integral part of The Unicode Standard, &lt;<link url='http://unicode.org/reports/tr9/'>http://unicode.org/reports/tr9/</link>&gt;.</note>" >
]>
<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
<xep>
<header>
  <title>Message Styling</title>
  <abstract>
    This specification defines a plain-text formatting syntax for use in
    exchanging instant messages with simple text styling.
  </abstract>
  &LEGALNOTICE;
  <number>xxxx</number>
  <status>ProtoXEP</status>
  <type>Standards Track</type>
  <sig>Standards</sig>
  <approver>Council</approver>
  <dependencies>
    <spec>XMPP Core</spec>
    <spec>XEP-0001</spec>
  </dependencies>
  <supersedes/>
  <supersededby/>
  <shortname>styling</shortname>
  &sam;
  <revision>
    <version>0.0.1</version>
    <date>2017-10-28</date>
    <initials>ssw</initials>
    <remark><p>First draft.</p></remark>
  </revision>
</header>
<section1 topic='Introduction' anchor='intro'>
  <p>
    Historically, XMPP has had no system for simple text styling.
    Instead, specifications like &xep0071; that require full layout engines have
    been used, leading to numerous security issues with implementations.
    Some clients have also performed their own formatting based on identifiers
    in the body.
    While this has worked well for those clients, it is not interoperable and
    leads to clients each supporting their own informal styling languages.
  </p>
  <p>
    This specification aims to provide a single, interoperable text styling
    language that can be used by entities that do not require full layout
    engines.
  </p>
</section1>
<section1 topic='Requirements' anchor='reqs'>
  <ul>
    <li>
      Clients that do not support this specification MUST still be able to
      receive messages sent by clients using this specification and display them
      in a human-readable form.
    </li>
    <li>
      Clients that support this specification MUST NOT be required to use a
      layout engine such as HTML or LaTeX.
    </li>
    <li>
      Messages formatted using this specification MUST NOT hinder readability on
      receiving clients regardless of client background color, contrast, or
      window size.
    </li>
    <li>
      Messages formatted using this specification MUST NOT hinder readability by
      users with color vision deficiency or impaired vision.
    </li>
    <li>
      Messages formatted with this specification MUST render correctly in
      locales with right-to-left (RTL) layouts without causing confusion.
    </li>
    <li>
      Clients that support this specification MUST NOT be required to extract
      metadata unrelated to formatting or text style from the message.
    </li>
    <li>
      Servers MUST NOT need to implement any new functionality for this
      specification to be supported.
    </li>
  </ul>
</section1>
<section1 topic='Glossary' anchor='glossary'>
  <p>
    Many important terms used in this document are defined in &unicode;.
    The terms "left-to-right" (LTR) and "right-to-left" (RTL) are defined in
    &uax9;.
  </p>
  <dl>
    <di>
      <dt>Formal markup language</dt>
      <dd>
        A structured markup language such as LaTeX, SGML, HTML, or XML that is
        formally defined and may include metadata unrelated to formatting or
        text style.
      </dd>
    </di>
    <di>
      <dt>Formatted text</dt>
      <dd>
        Text that includes non-textual information coded in a particular way
        that affects the interpretation of the text by computer programs
        (&rfc7764;).
      </dd>
    </di>
    <di>
      <dt>Plain text</dt>
      <dd>
        Text that does not convey any particular formatting or interpretation of
        the text by computer programs.
      </dd>
    </di>
    <di>
      <dt>Whitespace character</dt>
      <dd>
        Any Unicode scalar value which has the property "White_Space" or is in
        category Z in the Unicode Character Database.
      </dd>
    </di>
  </dl>
</section1>
<section1 topic='Use Cases' anchor='usecases'>
  <ul>
    <li>
      As an user sending an instant message to a friend, I want to be able to
      emphasize an important part of my message.
    </li>
    <li>
      As a software developer, I want to be able to send pre-formatted,
      monospace, block or inline text to another developer.
    </li>
    <li>
      As a multi-user chat user I want to quote something someone said earlier
      in the chat and make it evident that the text is a quotation.
    </li>
  </ul>
</section1>
<section1 topic='Discovering support' anchor='disco'>
  <section2 topic='Explicit Discovery' anchor='discovery-explicit'>
    <p>
      If an entity supports this specification it MUST advertise the fact by
      returning a feature of 'urn:xmpp:styling:0' &VNOTE; in response to a
      &xep0030; information request (or by advertising this namespace in the
      dynamic profile of service discovery defined in &xep0115;).
    </p>
    <example caption='Disco response'><![CDATA[
<iq type='result'
    from='viola@example.net/seashore-Iaqu8ith'
    to='captain@example.net/illyria-rohJa9au'
    id='Uw8riPhe'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    <feature var='urn:xmpp:styling:0' />
  </query>
</iq>
]]></example>
  </section2>
  <section2 topic='Implicit Discovery' anchor='discovery-implicit'>
    <p>
      An entity supporting this specification SHOULD render all messages
      &lt;body&gt; elements using this specification and MAY choose to send
      messages formatted using this specification even if the other end has not
      advertised support.
    </p>
  </section2>
</section1>
<section1 topic='Business Rules' anchor='rules'>
  <section2 topic='Display' anchor='display'>
    <p>
      Formatting characters MAY be displayed styled along with the span they
      apply to or they may be hidden and the styling only applied to the span.
      For instance, given the string "*emphasis*" both of the following are
      valid renderings:
    </p>
    <ul>
      <li><strong>*emphasis*</strong></li>
      <li><strong>emphasis</strong></li>
    </ul>
    <p>
      Examples in this document will display the formatting characters for
      clarity.
    </p>
  </section2>
  <section2 topic='Inlines' anchor='emph'>
    <p>
      Inline styling directives are evaluated lazily from the start of the byte
      stream (the left in left-to-right languages and the right in right-to-left
      languages).
      Matches MUST NOT extend over newlines and MUST start with a whitespace
      character or be the beginning of the line or the byte stream.
      Matches MUST contain some text between the two styling directives.
      Inline styling directives may also be doubled to allow the single
      character version of the directive to be styled.
      That is to say, "**emphasis**" is rendered the same as "*emphasis*".
      For example, the word "emphasized" would be styled in each of the
      following messages:
    </p>
    <ul>
      <li><strong>*emphasized*</strong></li>
      <li>foo <strong>*emphasized*</strong> bar</li>
      <li><strong>*emphasized*</strong>foo<strong>*emphasized*</strong></li>
      <li><strong>*emphasized*</strong>foo*</li>
      <li><strong>**emphasi*zed**</strong> foo*</li>
      <li>* <strong>*emphasized*</strong></li>
    </ul>
    <p>
      Nothing would be formatted in the following messages (where / represents a
      new line):
    </p>
    <ul>
      <li>not emphasized*</li>
      <li>*not emphasized</li>
      <li>*not / emphasized*</li>
      <li>**</li>
      <li>****</li>
    </ul>
  </section2>
  <section2 topic='Order of Operations' anchor='oporder'>
    <p>
      Block level styling such as preformatted blocks and quotations is always
      handled before inlines such as emphasis and inline preformatted text.
    </p>
  </section2>
  <section2 topic='Bold' anchor='bold'>
    <p>
      Text enclosed by '*' (U+002A ASTERISK) MUST be displayed with a greater
      weight than the surrounding text (bold face).
    </p>
    <example caption='Bold'><![CDATA[
<body>
  The full title is **Twelfth Night, or What You Will** but
  *most* people shorten it.
</body>
]]></example>
  </section2>
  <section2 topic='Italic' anchor='italic'>
    <p>
      Text enclosed by '_'(U+005F LOW LINE) MUST be displayed in italics.
    </p>
    <example caption='Italic'><![CDATA[
<body>
  The full title is _Twelfth Night, or What You Will_ but
  __most__ people shorten it.
</body>
]]></example>
  </section2>
  <section2 topic='Strike through' anchor='strike'>
    <p>
      Text enclosed by '~'(U+007E TILDE) MUST be displayed with a horizontal
      line through the middle (strike through).
    </p>
    <example caption='Strike through'><![CDATA[
<body>
  Everyone ~dis~likes cake.
</body>
]]></example>
  </section2>
  <section2 topic='Preformatted Inline Text' anchor='pre-inline'>
    <p>
      Text enclosed by a '`' (U+0060 GRAVE ACCENT) MUST be displayed inline in a
      monospace font.
      Inline formatting directives inside the inline preformatted text are not
      rendered.
      For example, in the following the word "monospace" is valid pre-formatted
      inline text:
    </p>
    <ul>
      <li>This is <tt>`monospace`</tt></li>
      <li>This is <tt>`*monospace*`</tt></li>
      <li>This is <strong><tt>*`monospace and bold`*</tt></strong></li>
    </ul>
    <example caption='Monospace text'><![CDATA[
<body>
  Wow, I can write in `monospace`, even a literal ``backtick (`)``!
</body>
]]></example>
  </section2>
  <section2 topic='Preformatted Block Text' anchor='pre-block'>
    <p>
      A block of text surrounded by lines consisting of a sequence of three
      backticks (U+0060 GRAVE ACCENT), "```", is preformatted text and should be
      displayed exactly as it was entered including whitespace.
      No other formatting described in this document should be rendered inside
      a preformatted text block.
    </p>
    <example caption='Preformatted block text'><![CDATA[
<body>
  ```
  (println &quot;Hello, world!&quot;)
  ```

  This should show up as monospaced, preformatted text ⤴
</body>
]]></example>
  </section2>
  <section2 topic='Quotations' anchor='quote'>
    <p>
      A quotation is indicated by one or more lines with a byte stream beginning
      with a '&gt;' (U+003E GREATER-THAN SIGN) immediately followed by a
      whitespace character.
      Inline formatting is rendered inside of quotations.
    </p>
    <example caption='Quotation (LTR)'><![CDATA[
<body>
  &gt; That that is, is.

  Said the old hermit of Prague.
</body>
]]></example>
    <example caption='Nested Quotation'><![CDATA[
<body>
  &gt;&gt; That that is, is.
  &gt; Said the old hermit of Prague.

  Who?
</body>
]]></example>
  </section2>
</section1>
<section1 topic='Implementation Notes' anchor='impl'>
  <p>
    The rules for inline styling form a context free grammar that cannot be
    matched by a regular expression.
    A simple stack based parser is recommended instead.
  </p>
</section1>
<section1 topic='Accessibility Considerations' anchor='access'>
  <p>
    When displaying text with formatting, developers should take care to ensure
    sufficient contrast exists between styled and unstyled text so that users
    with vision deficiencies are able to distinguish between the two.
  </p>
</section1>
<section1 topic='Internationalization Considerations' anchor='i18n'>
  <p>OPTIONAL.</p>
</section1>
<section1 topic='Security Considerations' anchor='security'>
  <p>REQUIRED.</p>
</section1>
<section1 topic='IANA Considerations' anchor='iana'>
  <p>
    This document requires no interaction with &IANA;.
  </p>
</section1>
<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
  <p>This specification defines the following XML namespaces:</p>
  <ul>
    <li>urn:xmpp:styling:0</li>
  </ul>
  <p>
    The &REGISTRAR; shall include the foregoing namespaces in its disco
    features registry as defined in &xep0030;.
  </p>
  <code caption='Registry Submission'><![CDATA[
<var>
  <name>urn:xmpp:styling:0</name>
  <desc>Indicates support for simple message styling.</desc>
  <doc>XEP-XXXX</doc>
</var>]]></code>
</section1>
<section1 topic='XML Schema' anchor='schema'>
  <p>This document does not define any new XML structure requiring a schema.</p>
</section1>
</xep>