docs: protected String idFor( File file ) {
          String path = file.getAbsolutePath();
          if (!path.startsWith(directoryAbsolutePath)) {
              if (directory.getAbsolutePath().equals(path)) {
                  // This is the root
                  return DELIMITER;
              }
              String msg = JcrI18n.fileConnectorNodeIdentifierIsNotWithinScopeOfConnector.text(getSourceName(), directoryPath, path);
              throw new DocumentStoreException(path, msg);
          }
          String id = path.substring(directoryAbsolutePathLength);
          id = id.replaceAll(Pattern.quote(FILE_SEPARATOR), DELIMITER);
          assert id.startsWith(DELIMITER);
          return id;
      }