docs: function hiddenByOverflow(e) {
      return bot.dom.getOverflowState(e) == bot.dom.OverflowState.HIDDEN &&
          goog.array.every(e.childNodes, function(n) {
            return !bot.dom.isElement(n) || hiddenByOverflow(n) ||
                   !positiveSize(n);
          });
    }