xml\:lang=, xml:lang

Namespaces are not supported for this format.
If there is an indication prior to this sentence that the browser supports namespaces, test passes if the background is  blue . Otherwise, test passes if the background is  yellow .

Text

Assertion: [Exploratory test] An xml\:lang= selector with a value that matches an xml:lang attribute value will not produce styling for documents served as XML if the browser supports namespace declarations, but will otherwise.

Notes:If the browser does support namespaces in selectors, a message to that effect will appear in the instructions line. The expectation would be that the test would change the background to yellow only if namespaces are not supported.
XHTML 1.0 as XML

selectors-071
Result summary & related tests