    return result;
    }
  }

  function finishCanContain(result) {
    var toSatisfy = canContain;
    if (toSatisfy instanceof Promise) {
      canContain = sortedMultiMap(result);
      // A limitation of our experimental framework is that it passes the body
      // of the document to the result function which means we can't really
      // test the relationship between the HTML and HEAD elements, for example.
      //
      // To work around that limitation, we hard code some canContain
      // relati