code: @Override
      public int compare(ILigand ligand1, ILigand ligand2) {
          int atomicNumberComp = atomicNumberRule.compare(ligand1, ligand2);
          if (atomicNumberComp != 0) return atomicNumberComp;
  
          int massNumberComp = massNumberRule.compare(ligand1, ligand2);
          if (massNumberComp != 0) return massNumberComp;
  
          if ("H".equals(ligand1.getLigandAtom().getSymbol())) {
              // both atoms are hydrogens
              return 0;
          }
  
          return massNumberComp;
      }
docs: {@inheritDoc}