Current spec has examples in 8.2.1, 8.2.2, and 8.3 with invalid syntax. 8.2.1 example:

  function handleKeyNeeded(event) {
    var video = event.target;
    var initData = event.initData;

    if (!video.keys)
      video.keys = MediaKeys("org.w3.clearkey");
    if (!video.keys)
      throw "Could not create MediaKeys";

    var keySession = mediaKeys.createSession(mimeType, initData);
    if (!keySession)
      throw "Could not create key session";

    keySession.onkeymessage="handleMessage(event)";
  }

"mediaKeys" does not map to a valid variable in this context and I assume should be "video.keys" since this matches the final example using MediaKeys in 8.4