The `rendition` Relation for HTML Links

Author: Garret Wilson
Version: 2012-02-14

Summary

The HTML specification defines a rel attribute for the <a>, <area>, and <link> elements indicating the relation of the target to the source. This specification defines one rel value, rendition, which indicates that the target is a some rendering, interpretation, or depiction of the source. User agents have great flexibility in presenting the target, including in-place actuation or navigation. Examples include audio pronunciations and visual depictions of mathematic formulas.

Description

The value rendition, when used as the rel attribute for the <a>, <area>, or <link> element, indicates that the target is a some rendering, interpretation, or depiction of the source. When used with <a> or <area> the rendition value indicates a rendering of the local source content; when used with <link> header it indicates a rendering of the entire document. The type attribute, if present, provides a hint as to the type of content the target represents.

User Agent Behavior

User agents have great flexibility in presenting a rendition target. Moreover, a user agent may determine the appropriate action based upon the provided type value, if any. Because a rendition is usually supplementary information, when the user actuates the link a user agent may attempt to execute or display the target information in-place rather than navigating to the target so as not to interrupt the flow of the primary content. Nevertheless, a user agent may always opt to navigate to a rendition target, allowing for backwards-compatibility with non-rendition-aware user agents.

Examples

Audio

If a rendition target is provided with an audio MIME content type, when the user actuates the link the user agent may decide to play the content in-place with no navigation. The following example provides an aural pronunciation both of a single letter and of an entire word.

<p>The Hindi letter <a href="ka.ogg" type="audio/ogg" rel="rendition">क</a> is used in the word <a href="kaam.ogg" type="audio/ogg" rel="rendition">काम</a>, which means <q>work</q>.</p>

Images

If a rendition target is provided with an image MIME content type, the user agent may choose to display the image as a flyover when the mouse is hovered over the link, or may may choose to display the image as a pop-up with no navigation when the link is actuated. The following example provides a visual representation of a formula for a sine wave.

<p>The formula <a href="sine.png" type="image/png" rel="rendition"><code>y=sin(x)</code></a> represents a sine wave.</p>

Inadequate Alternatives

Several alternatives to rel="rendition" were considered and abandoned as inadequate.

Link `rel="alternate"`

HTML already provides a rel value alternate, which indicates an alternate version of a resource. However, the semantics of alternate indicate that the target is an equivalent substitution of the indicated content. The value rendition instead indicates that the target is some interpretation or rendering of the content—an outcome, result, or example rather than an equivalent.

`<audio>` Element

HTML5 already provides an <audio> element which provides a reference of some audio that can be played by the user agent. The <audio> element has no means of relating the audio to a specific section of content as does a hyperlink. Moreover there exists no way to indicate the semantic relationship of the audio with the content. There is no simple declarative mechanism for allowing the user to explicitly actuate the audio in relation to the specified content as supplemental information. The <audio> element is furthermore limited to audio.

References

HTML5: Ian Hickson, editor. HTML5 Specification. World Wide Web Consortium, Working Draft 25 May 2011. (See http://www.w3.org/TR/html5/.)

The rendition Relation for HTML Links