docs: @Pure
  	public static File makeRelative(URL filenameToMakeRelative, URL rootPath) throws IOException {
  		if (filenameToMakeRelative == null || rootPath == null) {
  			throw new IllegalArgumentException();
  		}
  
  		final String basename = largeBasename(filenameToMakeRelative);
  		final URL dir = dirname(filenameToMakeRelative);
  
  		final String[] parts1 = split(dir);
  		final String[] parts2 = split(rootPath);
  
  		final String relPath = makeRelative(parts1, parts2, basename);
  
  		return new File(CURRENT_DIRECTORY, relPath);
  	}