Text alternatives for non-text content can be displayed in a variety of ways by a variety of user agents. Using synthetic speech, screen readers read the text aloud, helping people who do not see well or do not see at all. Such synthetic speech may also be helpful to people who have difficulty reading written text. Refreshable Braille displays present the text in tactile form for the benefit of people who depend on Braille. Conventional user agents such as desktop browsers include options to enhance legibility of text for people with limited vision by increasing or decreasing font size as well as changing text and background colors. People who cannot hear recorded speech can read transcripts. Providing text alternatives for non-text content thus makes it possible for people with different abilities using different devices to perceive the content of Web-based resources.
It is important to keep in mind that some people who depend on text alternatives do not have access to the non-text content. In other words, for many users the text alternative is not an "alternative" at all: the text alternative is the content. For other users, the text alternative is an important supplement to the non-text content.
When writing text alternatives it is important to ask yourself several questions about each piece of non-text content. For example:
What is the purpose of the non-text content?
Does it provide functionality (such as a graphical link or button)?
Does it convey information (such as a chart, diagram, or recording of a speech)?
Does it create a specific sensory experience, such as music without words or visual art?
If the non-text content does not provide functionality, convey information, or create a specific sensory experience, is it important for users to be aware of it?
The answers to these questions will help you determine what the text alternative should include, and may also lead to further questions.