The Role Attribute defined in this specification allows the author to annotate markup languages with machine-extractable semantic information about the purpose of an element. Use cases include accessibility, device adaptation, server-side processing, and complex data description. This attribute can be integrated into any markup language. In particular, schema implementations are provided to facilitate with languages based upon XHTML Modularization [XHTML-MODULARIZATION11-2e]. The role attribute is necessary to support Accessible Rich Internet Applications (WAI-ARIA) [WAI-ARIA] to define roles in XML-based languages, when the languages do not define their own role attribute. Although this is the reason the Role Attribute is published by the Protocols and Formats Working Group, the attribute has more general use cases as well.
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W3C Recommendations
Distributed and Interactive Systems

Pemberton, S., Adida, B., Birbeck, M., Raman, T. V., & Schwerdtfeger, R. (2012). Role Attribute 1.0. W3C Recommendations. W3C.