What is XML and how does it relate to accessibility?

XML is short for Extensible Markup Language and is a specification from the World Wide Web Consortium (W3C). It is a meta-syntax, used to define new markup languages. XML's key benefits are its extensibility (XML-based languages can be extended with new custom tags) and its portability (XML-based languages can be used across different platforms and devices).

XML can be good for accessibility. Many markup languages based on XML have been developed, or are currently under development, that are eliminating accessibility barriers. It should be noted, however, that the existence of a markup language that supports accessibility does not in and of itself make accessibility happen. It provides the foundation for accessibility, but only works if software tools (such as web browsers and assistive technologies) support it.

The following are a few examples of XML-based markup languages that can, or do, have a positive impact on accessibility:

• MathML—Provides a standard logical structure for the communication of mathematical expressions, allowing them, for example, to be displayed on web pages and read by screen readers.
• Timed Text Markup Language (TTML)—Provides a standard markup language for synchronizing text with media; for example for captions and subtitles
• Scalable Vector Graphics (SVG)—A language for describing two-dimensional graphics. SVG includes a number of accessibility features. For details, see SVG Accessibility Support, an appendix within the SVG specification.
• Voice Extensible Markup Language (VoiceXML)—A markup language for structuring interactive voice response applications. In order to make these applications accessible to users who are deaf or hard of hearing, the language provides a mechanism for including text alternatives to audio content.
• Comics XML—A simple markup language for comics, created by Jason McIntosh.