The word "type" seems to have crept unnecessarily into the title of this constraint; it's doing the same work as the much longer and hairier "Element Valid" constraint just above. However, attribute validity is such a rambling and detail-laden affair that there is no attempt to summarize it here as was done for elements.
Do note the important first phrase; an attribute must have been declared to be used in a valid document.
Copyright © 1998, Tim Bray. All rights reserved.