docs: def all_joined_units(self):
          """
          A list view of all the units of all relations attached to this
          :class:`~charms.reactive.endpoints.Endpoint`.
  
          This is actually a
          :class:`~charms.reactive.endpoints.CombinedUnitsView`, so the units
          will be in order by relation ID and then unit name, and you can access a
          merged view of all the units' data as a single mapping.  You should be
          very careful when using the merged data collections, however, and
          consider carefully what will happen when the endpoint has multiple
          relations and multiple remote units on each.  It is probably better to
          iterate over each unit and handle its data individually.  See
          :class:`~charms.reactive.endpoints.CombinedUnitsView` for an
          explanation of how the merged data collections work.
  
          Note that, because a given application might be related multiple times
          on a given endpoint, units may show up in this collection more than
          once.
          """
          if self._all_joined_units is None:
              units = chain.from_iterable(rel.units for rel in self.relations)
              self._all_joined_units = CombinedUnitsView(units)
          return self._all_joined_units