New Accessibility Guidelines Part III: Understandability
http://www.practicalecommerce.com/articles/1067-New-Accessibility-Guidelines-Part-III-Understandability

Dolson, Joseph C.
Practical eCommerce
2009

Abstract:

The understandability of text is crucial to web accessibility. At broad levels, this means specifying text languages, explaining the meanings of jargon or idioms, and expanding abbreviations to clarify text. It's not just text that can present a barrier to accessibility, however. A lack of organizational predictability or proper error management can greatly decrease the accessibility of any website.