Using ARIA: Roles, states, and properties

ARIA defines semantics that can be applied to elements, with these divided into roles (defining a type of user interface element) and states and properties that are supported by a role. Authors must assign an ARIA role and the appropriate states and properties to an element during its life-cycle, unless the element already has appropriate ARIA semantics (via use of an appropriate HTML element). Addition of ARIA semantics only exposes extra information to a browser's accessibility API, and does not affect a page's DOM.