C []A `xml:"X>Y"`
	}
	var wg sync.WaitGroup
	for i := 0; i < 2; i++ {
		wg.Add(1)
		go func() {
			Marshal(B{[]A{{}}})
			wg.Done()
		}()
	}
	wg.Wait()
}

func TestIsValidDirective(t *testing.T) {
	testOK := []string{
		"<>",
		"< < > >",
		"<!DOCTYPE '<' '>' '>' <!--nothing-->>",
		"<!DOCTYPE doc [ <!ELEMENT doc ANY> <!ELEMENT doc ANY> ]>",