Full description or summary of the content of an object such as a graphic, table, figure, or text box, typically used to make the object accessible.
The long description is a non-visual element used by systems such as pronouncing screen readers to make the object accessible to people or systems that cannot read/see/display the object.
Long Description Contents: This element contains a detailed textual description of a visual object, intended to convey the same information a sighted user would learn from looking at the object. For interchange purposes, the description should be in this element in the XML file. For display in web-based environments, it is common to put the textual content on a separate page from the main document, and point to that display page using a URL. Therefore, Best Practice is to incorporate a narrative textual description, including or ending with an untagged URI. The URI should then be repeated in an @xlink:href attribute, so that an actionable link can be made.
Accessibility: Please reserve this tag or accessibility uses such as pronouncing screen readers. The <long-desc> is not a visual element; rather, its purpose is to be spoken in circumstances where the visual form of the object cannot be viewed. This element differs from the <alt-text> element in both length and purpose. An <alt-text> is typically very short, for quick scan reading by a screen reader or showing as words behind a graphic. The <long-desc> is meant for an extended description of an object such as a figure, table, graphic, etc., for example, a textual summary of a pie chart that explains both the visual form of the chart and significance of its findings.
Best Practice: The <long-desc> element should not to be used as a replacement for <caption>, which is a visual element typically displayed alongside a figure, table, etc. Because a screen reader will pronounce the content of the <caption>, repeating the content of the <caption> in the <long-desc> is discouraged. If the <caption> or the test of the article adequately describe the meaning of the visual object, a <long-desc> is not required.
<!ELEMENT long-desc (#PCDATA %long-desc-elements;)* >
Expanded Content Model
(#PCDATA | x)*
This element may be contained in:
... <table-wrap> <caption> <title>The Size/Price Paradox</title> </caption> <long-desc>Table is a price comparison of some unknown objects that are identified only by color as Red and Green. The price of small, medium, and large objects is given for each color, with Green objects getting cheaper with increasing size, from $3.25 for small to $2.25 for medium to $1.15 for large. In contrast, Red objects get more expensive with size, with small costing $3.25, medium for $5.25, and large for $9.95. </long-desc> <table rules="rows"> <thead> <tr> <th>Color</th> <th>Size</th> <th>Price</th> </tr> </thead> <tbody> <tr> <td rowspan="3">Green</td> <td>small</td> <td>$3.25</td> </tr> <tr> <td>medium</td> <td>$2.25</td> </tr> <tr> <td>large</td> <td>$1.15</td> </tr> <tr> <td rowspan="3">Red</td> <td>small</td> <td>$3.25</td> </tr> <tr> <td>medium</td> <td>$5.25</td> </tr> <tr> <td>large</td> <td>$9.95</td> </tr> </tbody> </table> </table-wrap> ...