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Long Text Alternatives Why, When, and What

Why Use Long Text Alternatives?

Some types of complex images such as charts, graphs, and pictures can convey a significant amount of information visually or provide a specific sensory experience to a sighted person. These images can expand on statements made in a document; enhance understanding; or act as the central medium of information. Providing long text alternatives helps convey this information.

When to Use Long Text Alternatives

Long text alternatives can provide for rich, expressive documentation of a visual image and should be used when alt is insufficient to embody the visual qualities of an image.

If the short text alternative does not provide a text equivalent for the image, a long text alternative is also needed to supply supplemental content via a secondary mechanism.

To help decide whether a long text alternative is necessary turn off images in your browser and ask yourself:

Decision Tree Diagram: Does the short text alternative convey the information and meaning present in the image?

What Long Text Alternatives Provide in Contrast to the alt Attribute

User Choice

Screen readers read out the value of an alt attribute automatically. The old saying goes "a picture is worth a thousand words". While this is true, that doesn't mean everyone wants to hear all one thousand words at once or at this particular moment. Stuffing a long description into an alt attribute would force a screen reader user to listen to it.

In contrast the longdesc attribute provides users of screen readers such as JAWS the ability to pause, step outside of the page flow to obtain a description of a complex image. The difference is akin to glancing at a sophisticated chart or painting (alt functionality) versus studying it (longdesc functionality). Sighted users, have that choice (to glance or study). Long text alternatives offer that choice to users with disabilities.

Ability to Utilize Structured Markup

It is impossible to use links or structural markup with an alt attribute as its value only allows string text.

In contrast a long description can utilize headings, tables, lists, etcetera which can facilitate better communication and provide critical user functionality as discussed in the structure eClass.

Ability to Use a Separate Document

Using one global document to provide long descriptions for multiple instances of the same image is a powerful, portable, re-usable technique. It provides efficiency and scalability making authoring and maintenance easy wherever instances of the same image are used in multiple locations. It is analogous to the power of external style sheets.

One external file provides and controls the description for multiple docs.