Eio_utils.Nt_pathSourceWindows path syntax.
join dir step appends step to dir using "\\" as the directory separator, unless dir already ends in a separator. After a bare drive (C:) no separator is added, to keep the path drive-relative.split: Volume prefixes (C:, \\server\share, \\?\..., \??\...) are never split.is_relative p is true unless p begins with a volume or a separator. A drive-relative path such as C:x is not relative, since it is resolved against that drive's own current directory rather than ours.
dirname p is the directory part of p. It is "." when p names something in the current directory, and also when p has no parent to name (e.g. the empty path, a bare volume (C:) and a root (\\server\share)).
basename p is the final component of p. It is p itself when p has no directory part, and "." when p is empty.
to_nt ~cwd path is the NT object-manager form of the Win32 path path.
A relative path is resolved against cwd and, as in Win32, "/" is a separator and "." and ".." components are removed. Verbatim (\\?\...) and NT (\??\...) paths are passed through unchanged.