docs: def set_maxrad(self,newrad):
          """
          Sets max allowed radius in populations.
  
          Doesn't operate via the :class:`stars.Constraint`
          protocol; rather just rescales the sky positions
          for the background objects and recalculates
          sky area, etc.
  
          """
          if not isinstance(newrad, Quantity):
              newrad = newrad * u.arcsec
          #if 'Rsky' not in self.constraints:
          #    self.constraints.append('Rsky')
          for pop in self.poplist:
              if not pop.is_specific:
                  try:
                      pop.maxrad = newrad
                  except AttributeError:
                      pass