docs: function _checkKeysFromFirstAreInSecond(first, second) {
      for (var key in first) {
          if (!(key in second)) {
              return false;
          }
  
          var value1 = first[key];
          var value2 = second[key];
  
          if (!deepEquals(value1, value2)) {
              return false;
          }
      }
  
      return true;
  }