Check the basic attribute support of CSSOM CSSNamespaceRule On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE". PASS CSSRule.NAMESPACE_RULE is 10 PASS namespacerule.type is 10 PASS namespacerule.namespaceURI is "http://www.w3.org/1999/xhtml" PASS namespacerule.prefix is "my-namespace" PASS defaultNamespacerule.cssText is "@namespace url(\"default\");" PASS namespacerule.cssText is "@namespace my-namespace url(\"http://www.w3.org/1999/xhtml\");" PASS getComputedStyle(document.body).color is "rgb(255, 0, 0)" Deleting namespace rule when other rules are present should throw InvalidStateException. WARN: shouldBe() expects string arguments PASS 11 is 11 Inserting new namespace rule when other rules are present should throw InvalidStateException. WARN: shouldBe() expects string arguments PASS 11 is 11 PASS successfullyParsed is true TEST COMPLETE Here is some text!