The only things I can think of is the use of newtypes around PathBuf that enforces things like expansion and that makes the check for you when restricting tk a

The only things I can think of is the use of newtypes around PathBuf that enforces things like expansion and that makes the check for you when restricting tk a specific directory. Now that I'm writing this out, this feels like it could be a very useful small crate or addition to Camino. Thank you for making me think further about this. Of course, the impl would have an associated runtime cost for the check and a more involved API surface because it's asking the developer for more information. But once you do that you can have an TryInto<PathBuf> impl to pass it to any standard method.