docs: def in_casapy (helper, vis=None, figfile=None):
      """This function is run inside the weirdo casapy IPython environment! A
      strange set of modules is available, and the
      `pwkit.environments.casa.scripting` system sets up a very particular
      environment to allow encapsulated scripting.
  
      """
      if vis is None:
          raise ValueError ('vis')
  
      helper.casans.plotants (vis=vis, figfile=figfile)