 experiment framework passes the body element so there's no
        // need for an explicit body tag on the stack.
        return [];
      }
      var memoKey = opt_exclusions
          ? elementName + ' ' + opt_exclusions.join(' / ') : elementName;

      if (getOwn(canAppearInBody, elementName)) { return [elementName]; }
      var prior = getOwn(memoKey, elementName, void 0);
      if (prior !== void 0) { return prior ? prior.slice() : null; }
      var empty = [];

      function end(e) {
        return