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In the HTML5 spec: http://www.w3.org/TR/html5/interactive-elements.html#selectors There is a list of attributes which are case insensitive. This includes many of the compact/minimized/boolean attributes of HTM4 such as readonly, disabled, checked etc. Currently with the implementations I tested, the boolean attributes for audio and video are case insensitive but not listed here. These include autoplay, loop and controls. It may be simpler to have a statement here that just includes all of these kinds of attributes.
This list is about attribute *values*, not attribute *names*. Gecko, WebKit and Presto interoperably treat the values of video@autoplay as case-sensitive. See <http://software.hixie.ch/utilities/js/live-dom-viewer/saved/440>.
You are correct. I was speaking of the values however I misspoke about other browser support.