Assertion: A :lang value with a multiple subtags will match a xml:lang attribute value with multiple subtags as long as the first part is the same.

Notes:
You can only get meaningful results for this test if :lang works with xml:lang, since it checks a detail with regard to that support. If :lang does not work with xml:lang, the test should show a message "Ignore this test." You should ignore the instructions and test results that follow and mark the results as "not applicable".