ar v = 3000 * emToPx;
      assert_approx_equals(getBox("ref0006").top - getBox("num0006").bottom,
                           v, epsilon, "mfrac: numerator shift");
    }, "TopDisplayStyleShiftUp");

    test(function() {
      assert_true(MathMLFeatureDetection.has_mspace());

      var v = 3000 * emToPx;
      assert_approx_equals(getBox("ref0006b").top - getBox("num0006b").bottom,
                           v, epsilon, "mfrac: numerator shift");
    }, "TopDisplayStyleShiftUp Displaystyle");

    test(fu