code: public final CellName clusteringKey(CellName cellName) {
          CBuilder builder = cellNameType.builder();
          for (int i = 0; i < metadata.clusteringColumns().size(); i++) {
              ByteBuffer component = cellName.get(i);
              builder.add(component);
          }
          Composite prefix = builder.build();
          return cellNameType.rowMarker(prefix);
      }
docs: Returns the clustering key contained in the specified {@link CellName}.
  
  @param cellName A {@link CellName}.
  @return The clustering key contained in the specified {@link CellName}.