docs: def prior(self):
          """
          Model prior for particular model.
  
          Product of eclipse probability (``self.prob``),
          the fraction of scenario that is allowed by the various
          constraints (``self.selectfrac``), and all additional
          factors in ``self.priorfactors``.
  
          """
          prior = self.prob * self.selectfrac
          for f in self.priorfactors:
              prior *= self.priorfactors[f]
          return prior