docs: function (axisModel, ecModel, api) {
  
          var dim = this.dimension;
  
          var axis = new SingleAxis(
              dim,
              axisHelper.createScaleByModel(axisModel),
              [0, 0],
              axisModel.get('type'),
              axisModel.get('position')
          );
  
          var isCategory = axis.type === 'category';
          axis.onBand = isCategory && axisModel.get('boundaryGap');
          axis.inverse = axisModel.get('inverse');
          axis.orient = axisModel.get('orient');
  
          axisModel.axis = axis;
          axis.model = axisModel;
          axis.coordinateSystem = this;
          this._axis = axis;
      }