Message Styling

%ents; RFC 7764 RFC 7764: Guidance on Markdown: Design Philosophies, Stability Strategies, and Select Registrations <http://tools.ietf.org/html/rfc7764>." > Unicode Standard Annex #9 Unicode Standard Annex #9, "Unicode Bidirectional Algorithm", edited by Mark Davis, Aharon Lanin, and Andrew Glass. An integral part of The Unicode Standard, <http://unicode.org/reports/tr9/>." > ]>

Message Styling This specification defines a plain-text formatting syntax for use in exchanging instant messages with simple text styling. &LEGALNOTICE; xxxx ProtoXEP Standards Track Standards Council XMPP Core XEP-0001 styling &sam; 0.0.1 2017-10-28 ssw

First draft.

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.

This specification aims to provide a single, interoperable text styling language that can be used by entities that do not require full layout engines.

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.
Clients that support this specification MUST NOT be required to use a layout engine such as HTML or LaTeX.
Messages formatted using this specification MUST NOT hinder readability on receiving clients regardless of client background color, contrast, or window size.
Messages formatted using this specification MUST NOT hinder readability by users with color vision deficiency or impaired vision.
Messages formatted with this specification MUST render correctly in locales with right-to-left (RTL) layouts without causing confusion.
Clients that support this specification MUST NOT be required to extract metadata unrelated to formatting or text style from the message.
Servers MUST NOT need to implement any new functionality for this specification to be supported.

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;.

Formal markup language: 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.
Formatted text: Text that includes non-textual information coded in a particular way that affects the interpretation of the text by computer programs (&rfc7764;).
Plain text: Text that does not convey any particular formatting or interpretation of the text by computer programs.
Whitespace character: Any Unicode scalar value which has the property "White_Space" or is in category Z in the Unicode Character Database.

As an user sending an instant message to a friend, I want to be able to emphasize an important part of my message.
As a software developer, I want to be able to send pre-formatted, monospace, block or inline text to another developer.
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.

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;).

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An entity supporting this specification SHOULD render all messages <body> elements using this specification and MAY choose to send messages formatted using this specification even if the other end has not advertised support.

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:

*emphasis*
emphasis

Examples in this document will display the formatting characters for clarity.

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:

*emphasized*
foo *emphasized* bar
*emphasized*foo*emphasized*
*emphasized*foo*
**emphasi*zed** foo*
* *emphasized*

Nothing would be formatted in the following messages (where / represents a new line):

not emphasized*
*not emphasized
*not / emphasized*
**
****

Block level styling such as preformatted blocks and quotations is always handled before inlines such as emphasis and inline preformatted text.

Text enclosed by '*' (U+002A ASTERISK) MUST be displayed with a greater weight than the surrounding text (bold face).

The full title is **Twelfth Night, or What You Will** but *most* people shorten it. ]]>

Text enclosed by '_'(U+005F LOW LINE) MUST be displayed in italics.

The full title is _Twelfth Night, or What You Will_ but __most__ people shorten it. ]]>

Text enclosed by '~'(U+007E TILDE) MUST be displayed with a horizontal line through the middle (strike through).

Everyone ~dis~likes cake. ]]>

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:

This is `monospace`
This is `*monospace*`
This is *`monospace and bold`*

Wow, I can write in `monospace`, even a literal ``backtick (`)``! ]]>

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.

``` (println "Hello, world!") ``` This should show up as monospaced, preformatted text ⤴ ]]>

A quotation is indicated by one or more lines with a byte stream beginning with a '>' (U+003E GREATER-THAN SIGN) immediately followed by a whitespace character. Inline formatting is rendered inside of quotations.

> That that is, is. Said the old hermit of Prague. ]]> >> That that is, is. > Said the old hermit of Prague. Who? ]]>

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.

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.

OPTIONAL.

REQUIRED.

This document requires no interaction with &IANA;.

This specification defines the following XML namespaces:

urn:xmpp:styling:0

The ®ISTRAR; shall include the foregoing namespaces in its disco features registry as defined in &xep0030;.


  urn:xmpp:styling:0
  Indicates support for simple message styling.
  XEP-XXXX
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This document does not define any new XML structure requiring a schema.