docs: function(hierarchyIndexOrName){
          if (_isUnd(hierarchyIndexOrName)) index = this._hierarchyIndex;
          var index, hierarchyName, hierarchy;
          if (_isNum(hierarchyIndexOrName)) {
              if (hierarchyIndexOrName !== parseInt(hierarchyIndexOrName, 10)
              ||  hierarchyIndexOrName >= this.numHierarchies
              )
                  Xmla.Exception._newError(
                      "INVALID_HIERARCHY",
                      "Xmla.Dataset.Axis.hierarchyDef",
                      hierarchyIndexOrName
                  )._throw();
              hierarchyName = this.hierarchyName(hierarchyIndexOrName);
          }
          else hierarchyName = hierarchyIndexOrName;
          hierarchy = this._hierarchyDefs[hierarchyName];
          if (_isUnd(hierarchy))
              Xmla.Exception._newError(
                  "INVALID_HIERARCHY",
                  "Xmla.Dataset.Axis.hierarchyDef",
                  hierarchyName
              )._throw();
          return hierarchy;
      }