docs: protected File fileFor( String id ) {
          assert id.startsWith(DELIMITER);
          if (id.endsWith(DELIMITER)) {
              id = id.substring(0, id.length() - DELIMITER.length());
          }
          if (isContentNode(id)) {
              id = id.substring(0, id.length() - JCR_CONTENT_SUFFIX_LENGTH);
          }
          return new File(directory, id);
      }