ert_true(MathMLFeatureDetection.has_operator_spacing());
              var mrow = document.getElementById(tag);
              var mn1 = mrow.firstElementChild.getBoundingClientRect();
              var mn2 = mrow.lastElementChild.getBoundingClientRect();
              assert_greater_than_equal(mn2.left - mn1.right, 50);
          }, `operator spacing inside ${tag}`);
      });
      done();
  }
</script>
</head>
<body>
  <div id="log"></div>
  <p>
    <math><mrow id="Mrow"><mn>1</mn><mo lspace="50px">|</mo>