code: private boolean tryPath(StringBuilder prefix, String el, boolean dir) {
      String path = prefix + "/" + el;
  
      if (dir && directoryBrowsingDisallowed) {
        path += "/" + xsltdirMarkerName;
      }
  
      if (debug()) {
        debug("trypath: " + path);
      }
  
      try {
        URL u = new URL(path);
  
        URLConnection uc = u.openConnection();
  
        if (!(uc instanceof HttpURLConnection)) {
          return false;
        }
  
        HttpURLConnection huc = (HttpURLConnection)uc;
  
        if (huc.getResponseCode() != 200) {
          return false;
        }
  
        prefix.append("/");
        prefix.append(el);
  
        return true;
      } catch (final Throwable t) {
        if (debug()) {
          debug("trypath exception: ");
          error(t);
        }
      }
  
      return false;
    }
docs: Try a path and see if it exists. If so append the element
  
  @param   prefix    StringBuilder current path prefix
  @param   el        String path element to append
  @param   dir       true if el is a directory
  @return  boolean   true if path is OK