The "List of event handler content attributes" index at http://dev.w3.org/html5/spec/section-index.html#ix-event-handlers is missing the onreadystatechange attribute.
This bug was cloned to create bug 17822 as part of operation convergence.
see comment https://www.w3.org/Bugs/Public/show_bug.cgi?id=17822#c2 from Hixie
"Turns out this isn't an error, since it's not a content attribute and the index is only content attributes."
onreadystatechange is not a valid content attribute