
FAIL "is" value should be serialized if the custom element has no "is" content attribute function is not a constructor (evaluating 'super(...args)')
FAIL "is" value should be serialized even for an undefined element assert_equals: expected "<p is=\"your-p\"></p>" but got "<p></p>"
PASS "is" content attribute should be serialized even if the element is a customized built-in element