code: function getCommonType(elems) {
          if (elems && elems.length > 0) {
              var commonType = elems[0].getClass();
              while (!_.every(elems, function (e) { return (e instanceof commonType); })) {
                  commonType = getSuperType(commonType);
              }
              return commonType;
          } else {
              return null;
          }
      }
docs: Return a generalized type of given elements.
  
  @param {Array.<Element>} elems
  @return {constructor}