code: def add_limit(self, label='0_0', **props):
          
  
          if label not in self.leaf_labels:
              raise ValueError('No model node named {} (must be in {}). Maybe define models first?'.format(label, self.leaf_labels))
          for k,v in props.items():
              if k not in self.spec_props:
                  raise ValueError('Illegal property {} (only {} allowed).'.format(k, self.spec_props))
              if len(v) != 2:
                  raise ValueError('Must provide (min, max) for {}. (`None` is allowed value)'.format(k))
  
          if label not in self.limits:
              self.limits[label] = {}
  
          for k,v in props.items():
              vmin, vmax = v
              if vmin is None:
                  vmin = -np.inf
              if vmax is None:
                  vmax = np.inf
              self.limits[label][k] = (vmin, vmax)
  
          self._clear_cache()
docs: Define limits to spectroscopic property of particular stars.
  
          Usually will be used for 'logg', but 'Teff' and 'feh' will also work.
  
          In form (min, max): e.g., t.add_limit(logg=(3.0,None))
  
          None will be converted to (-)np.inf