Table of Contents

• Introduction
• 1. Conformance
  • 1.1 Dependencies
• 2. Use Cases and Requirements
• 3. The longdesc Attribute
  • 3.1 Extensions to the HTMLImageElement interface
    • 3.1.1 Attributes
• A. Acknowledgements
• B. References
  • B.1 Normative references
  • B.2 Informative references

1. Conformance

As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.

The key words must, should, and may in this specification are to be interpreted as described in [RFC2119].

Requirements phrased in the imperative as part of algorithms (such as "strip any leading space characters" or "return false and terminate these steps") are to be interpreted with the meaning of the key word ("must", "should", "may", etc) used in introducing the algorithm.

Conformance requirements phrased as algorithms or specific steps may be implemented in any manner, so long as the end result is equivalent. (In particular, the algorithms defined in this specification are intended to be easy to follow, and not intended to be performant.)

When a method or an attribute is said to call another method or attribute, the user agent must invoke its internal API for that attribute or method so that e.g. the author can't change the behavior by overriding attributes or methods with custom properties or functions in ECMAScript.

If an algorithm calls into another algorithm, any exception that is thrown by the latter (unless it is explicitly caught), must cause the former to terminate, and the exception to be propagated up to its caller.

2. Use Cases and Requirements

There are many ways to ensure that users do not need to see images in order to successfully interact with content. The alt attribute is designed to ensure that for everyday work, a user has enough information to replace an image, and often this is more helpful than a detailed description of every image.

@@This needs to be completed - I have content to add (there has been a lot of discussion of this over the years).

3. The longdesc attribute

partial interface HTMLImageElement {
             attribute DOMString longdesc;
};

//Make the first internal longdesc reference absolute

var baseURL = document.location.origin + document.location.pathname
var someImage = document.querySelector('img[longdesc^=#]');

someImage.longdesc = baseURL + someImage.longdesc;

//Open new windows for each longdesc found

var describedImages = document.querySelectorAll('[longdesc]');

for (i in describedImages) {
  if (i.longdesc) //there are a couple of extra things matched 
    window.open(i.longdesc);
}