New Accessibility Guidelines Part II: Operability
http://www.practicalecommerce.com/articles/1024-New-Accessibility-Guidelines-Part-II-Operability

Dolson, Joseph C.
Practical eCommerce
2009

Abstract:

The concept behind website operability is simple: Can everybody use the tools and mechanisms required to operate your website? Operability may seem easy, but it can be very challenging. Every control, every link, and every button on your site is a potential point of failure for operability. Without appropriate consideration for the disabled, you run the risk that disabled users will be unable to access your site.