code: private Block addItemBlock(Block currentBlock, HeaderBlock headerBlock, String documentReference)
      {
          ListItemBlock itemBlock =
              headerBlock == null ? createEmptyTocEntry() : createTocEntry(headerBlock, documentReference);
  
          currentBlock.addChild(itemBlock);
  
          return itemBlock;
      }
docs: Add a {@link ListItemBlock} in the current toc tree block and return the new {@link ListItemBlock}.
  
  @param currentBlock the current block in the toc tree.
  @param headerBlock the {@link HeaderBlock} to use to generate toc anchor label.
  @return the new {@link ListItemBlock}.