code: function (node, name, expected) {
      {
        if (!isAttributeNameSafe(name)) {
          return;
        }
        if (!node.hasAttribute(name)) {
          return expected === undefined ? undefined : null;
        }
        var value = node.getAttribute(name);
        if (value === '' + expected) {
          return expected;
        }
        return value;
      }
    }
docs: Get the value for a attribute on a node. Only used in DEV for SSR validation.
  The third argument is used as a hint of what the expected value is. Some
  attributes have multiple equivalent values.