michael@0: :not(output).invalid-ref {
michael@0:   box-shadow: 0 0 1.5px 1px red;
michael@0: }
michael@0: 
michael@0: :not(output):-moz-focusring.invalid-ref {
michael@0:   box-shadow: 0 0 2px 2px rgba(255,0,0,0.4);
michael@0: }
michael@0: 
michael@0: output.invalid-ref {
michael@0:   color: red;
michael@0: }
michael@0: 
michael@0: .barred-ref {
michael@0: }