code: function(){
          var hierarchyNames = [], i, n = this.numHierarchies;
          for (i = 0; i < n; i++) hierarchyNames[i] = this._hierarchyOrder[i];
          return hierarchyNames;
      }
docs: Returns the names of the hierarchies of this Axis object.
  @method getHierarchyNames
  @return {array} An array of names of the hierarchies contained in this Axis.