docs: def tunable(self, obj):
          """A tunable resource maps against a backend..."""
          self.tune = dict()
          if 'tune' in obj:
              for tunable in MOUNT_TUNABLES:
                  tunable_key = tunable[0]
                  map_val(self.tune, obj['tune'], tunable_key)
                  if tunable_key in self.tune and \
                     is_vault_time(self.tune[tunable_key]):
                      vault_time_s = vault_time_to_s(self.tune[tunable_key])
                      self.tune[tunable_key] = vault_time_s
  
          if 'description'in obj:
              self.tune['description'] = obj['description']