URI Formats

Hello, do you have documentation on the usage/formats of URIs for Language Providers? 

In particular, we'd like guidance on how many "/"s are needed when "building" the URIs, in a file based context. 

We've noticed that things can work when we put up to 5 slashes in the URI for AnyTMs and/or sometimes in the plain sdltm.file context

What are the rules?