docs: def delete(self, data_src):
          """
          Delete data sources.
          """
          items = self.objects[data_src].data.keys()  # items to edit
          self.reg.unregister(items)  # remove items from Registry
          self.layer.pop(data_src)  # remove data source from layer
          self.objects.pop(data_src)  # remove data_source object
          self.sources.pop(data_src)