code: def boolean_add(self, mesh, inplace=False):
          
          vtkappend = vtk.vtkAppendPolyData()
          vtkappend.AddInputData(self)
          vtkappend.AddInputData(mesh)
          vtkappend.Update()
  
          mesh = _get_output(vtkappend)
          if inplace:
              self.overwrite(mesh)
          else:
              return mesh
docs: Add a mesh to the current mesh.  Does not attempt to "join"
          the meshes.
  
          Parameters
          ----------
          mesh : vtki.PolyData
              The mesh to add.
  
          inplace : bool, optional
              Updates mesh in-place while returning nothing.
  
          Returns
          -------
          joinedmesh : vtki.PolyData
              Initial mesh and the new mesh when inplace=False.