What standards exist for developing and purchasing accessible software?

DO-IT Factsheet #1098
http://www.washington.edu/accessit/articles?1098

When making software procurement decisions, educational entities need to look critically at which products in a given software category will best serve the needs of all students, without excluding some on the basis of disability. To determine whether a software application is accessible, the application should be evaluated according to a set of guidelines or standards that defines software accessibility.

The only legal standard is Section 1194.21 ("Software applications and operating systems") of Electronic and Information Technology Accessibility Standards [1]. These standards were developed by the Access Board as required by Section 508 of the Rehabilitation Act Amendments of 1998. There are twelve standards, and the Access Board provides a detailed explanation of each in its Guide to the Standards [2].

Additional guidelines and resources are provided in the AccessIT Knowledge Base article How can I tell whether a software application is accessible? [3]

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