code: @Override
      protected void _from(ObjectInput in) throws IOException,
              ClassNotFoundException {
          // 1: read the number of document headers
          final int size = in.readInt();
          headers = sizedArrayList(size);
          for (int i = 0; i < size; ++i) {
              final DocumentHeader header = new DocumentHeader();
              // 1: read each document header
              header.readExternal(in);
              addDocumentHeader(header);
          }
      }
docs: {@inheritDoc}