docs: public static DefaultFileSet copy(FileSet source, BaseFolder target, String manifestFileName) throws IOException {
  		Path manifestFolder = target.getPath().resolve(source.getManifestPath()).getParent();
  		Path manifestPath = manifestFolder.resolve(manifestFileName);
  		if (!manifestPath.getParent().equals(manifestFolder)) {
  			throw new IllegalArgumentException("Illegal characters in file name: " + manifestFileName);
  		}
  		String manifestPathString = target.getPath()
  				.relativize(manifestPath)
  				.normalize()
  				.toString();
  		return copyInner(source, manifestPathString, target);
  	}