Core Accessibility API Mappings 1.1 is a recommendation provided by the World Wide Web Consortium (W3C) that aims to standardize the way in which user agents expose semantics of web content languages to accessibility APIs. Quoting the specification, “This helps users with disabilities to obtain and interact with information using assistive technologies. Documenting these mappings promotes interoperable exposure of roles, states, properties, and events implemented by accessibility APIs and helps to ensure that this information appears in a manner consistent with author intent.”
Note that this can be considered an “advanced” specification, as it is aimed specifically at assistive technology and user agent developers; yet, you may find it useful in order to understand how web content will be perceived by assistive technology users across different platforms and operating systems. It also gives you a deep understanding on how accessibility works “under the hood”.