As I understand - there is currently no way to track metadata for directories with git annex metadata (it only works for files). Is that indeed the case?

One workaround I'm looking at is to add a metadata placeholder file for directory metadata inside the directory. As I understand - each directory would need to have such file with some unique content (perhaps UUID), otherwise metadata between files for different directories will actually collide. Are there alternatives/better solutions for tracking datasets metadata (groups of files in a folder)?