The GlobalMentor core library already defines . and .. for URIs as current-level and parent-level path segments in com.globalmentor.net.URIs. We need something similar to refer to paths and files outside the context of a URI. These definitions would most likely go in com.globalmentor.io.Filenames.
As noted in the API docs for Path.normalize():
In many file systems, the "." and ".." are special names used to indicate the current directory and parent directory.
That is, these apparently are not necessarily special names on all implementations of FileSystem. Nevertheless they are special on the overwhelming majority of file systems, as discussed on Stack Overflow (one answer to which includes one hack that might be used to determine if they are special or not on a given file system).