docs: def detached_sites( self, site_labels=None ):
          """
          Returns all sites in the lattice (optionally from the set of sites with specific labels)
          that are not part of a percolating network.
          This is determined from clusters of connected sites that do not wrap round to
          themselves through a periodic boundary.
  
          Args:
              site_labels (String or List(String)): Lables of sites to be considered.
  
          Returns:
              (List(Site)): List of sites not in a periodic percolating network.
          """
          clusters = self.connected_sites( site_labels=site_labels )
          island_clusters = [ c for c in clusters if not any( c.is_periodically_contiguous() ) ]
          return list( itertools.chain.from_iterable( ( c.sites for c in island_clusters ) ) )