docs: def _register_plotter(cls, identifier, module, plotter_name,
                            plotter_cls=None):
          """
          Register a plotter in the :class:`Project` class to easy access it
  
          Parameters
          ----------
          identifier: str
              Name of the attribute that is used to filter for the instances
              belonging to this plotter
          module: str
              The module from where to import the `plotter_name`
          plotter_name: str
              The name of the plotter class in `module`
          plotter_cls: type
              The imported class of `plotter_name`. If None, it will be imported
              when it is needed
          """
          if plotter_cls is not None:  # plotter has already been imported
              def get_x(self):
                  return self(plotter_cls)
          else:
              def get_x(self):
                  return self(getattr(import_module(module), plotter_name))
          setattr(cls, identifier, property(get_x, doc=(
              "List of data arrays that are plotted by :class:`%s.%s`"
              " plotters") % (module, plotter_name)))
          cls._registered_plotters[identifier] = (module, plotter_name)