code: def on_lstCanvasAggLayers_itemSelectionChanged(self):
          
          self.parent.aggregation_layer = self.selected_canvas_agglayer()
          lblText = self.parent.get_layer_description_from_canvas(
              self.parent.aggregation_layer, 'aggregation')
          self.lblDescribeCanvasAggLayer.setText(lblText)
          self.parent.pbnNext.setEnabled(True)
docs: Update layer description label.
  
          .. note:: This is an automatic Qt slot
             executed when the category selection changes.