docs: def verify_identifiers(identifiers, n_items):
      """Ensure that identifiers has a compatible length and that its elements
      are unique"""
      if identifiers is None:
          return identifiers
  
      identifiers = np.array(identifiers, copy=False)
  
      # Check length for consistency
      if len(identifiers) != n_items:
          raise ValueError("identifiers has inconsistent dimension.")
  
      # Check that identifiers are unique
      if len(np.unique(identifiers)) != n_items:
          raise ValueError("identifiers contains duplicate values.")
  
      return identifiers