In December, 2013, the W3C Schema.org process accepted a proposal for a set of accessibility metadata terms based on the AccessForAll specification. The accessibility metadata is now a part of the Schema.org CreativeWork properties.
Schema.org was created by a consortium of large search engines (including Google, Yahoo, etc.) as a collection of schemas that can be used to add semantic information to content and improve search results. The inclusion of accessibility metadata in the Schema.org collection would help people to easily find content that meets their individual needs and preferences.
This accessibility metadata can be embedded directly in the markup of any web content. The example below shows how a page that includes a video and audio file might use the accessibility metadata properties:
<h1>Martin Luther King's Speech: 'I Have a Dream'</h1>
<div id="videoMLK" itemprop="video">
<p class="alert">Warning: This video contains
<span itemprop="accessHazard">flashing</span> that
may cause seizures in some individuals. The
<a itemprop="hasAdaptation" href="#mlkAudio">audio
track of the speech</a> is separately available
below as an alternative.</p>
<video src="http://www.youtube.com/watch?v=smEqnnklfYs" controls="">
<track src="captions.webvtt" type="captions"/>
<div itemprop="transcript" id="transcriptMLK">
<meta itemprop="displayTransformability" content="css"/>
You can find the complete list of proposed properties, as well as more information and examples, at http://www.a11ymetadata.org/.