code: function(hierarchyName){
          if (_isUnd(hierarchyName)) return this._hierarchyIndex;
          var index = this._hierarchyIndexes[hierarchyName];
          if (_isUnd(index))
              Xmla.Exception._newError(
                  "INVALID_HIERARCHY",
                  "Xmla.Dataset.Axis.hierarchyDef",
                  hierarchyName
              )._throw();
          return index;
      }
docs: Gets the index of the hierarchy identified by the specified name, or the index of the current hierarchy (in case the name argument is omitted).
  @method hierarchyIndex
  @param hierarchyName {string} The name of the hierarchy for which the index is to be retrieved. When omitted, the index of the current hierarchy is returned.
  @return {int} The index of the hierarchy specified by the name passed as argument, or the index of the current hierarchy if the name argument is omitted.