code: def default_spec(self, manager):
          
          # TODO: I feel like this + the surrounding bits in add_to_manager()
          # could be consolidated & simplified...
          specstr = ""
          # Make sure truly-default spec skips 0.x if prehistory was unstable.
          stable_families = manager.stable_families
          if manager.config.releases_unstable_prehistory and stable_families:
              specstr = ">={}".format(min(stable_families))
          if self.is_featurelike:
              # TODO: if app->config-><releases_always_forwardport_features or
              # w/e
              if True:
                  specstr = ">={}".format(max(manager.keys()))
          else:
              # Can only meaningfully limit to minor release buckets if they
              # actually exist yet.
              buckets = self.minor_releases(manager)
              if buckets:
                  specstr = ">={}".format(max(buckets))
          return Spec(specstr) if specstr else Spec()
docs: Given the current release-lines structure, return a default Spec.
  
          Specifics:
  
          * For feature-like issues, only the highest major release is used, so
            given a ``manager`` with top level keys of ``[1, 2]``, this would
            return ``Spec(">=2")``.
  
              * When ``releases_always_forwardport_features`` is ``True``, that
                behavior is nullified, and this function always returns the empty
                ``Spec`` (which matches any and all versions/lines).
  
          * For bugfix-like issues, we only consider major release families which
            have actual releases already.
  
              * Thus the core difference here is that features are 'consumed' by
                upcoming major releases, and bugfixes are not.
  
          * When the ``unstable_prehistory`` setting is ``True``, the default
            spec starts at the oldest non-zero release line. (Otherwise, issues
            posted after prehistory ends would try being added to the 0.x part of
            the tree, which makes no sense in unstable-prehistory mode.)