I tested attribute parsing, createAttribute and setAttribute in Opera, Firefox and Internet Explorer. <http://annevankesteren.nl/test/dom/html/attr/001> <http://annevankesteren.nl/test/dom/html/attr/002> <http://annevankesteren.nl/test/dom/html/attr/003>
It seems that Firefox lowercases all unknown and known attributes. It seems that Opera and Internet Explorer lowercase all known attributes unless they are created using createAttribute. Opera and Internet Explorer do not touch unknown attributes. -- Anne van Kesteren <http://annevankesteren.nl/>