Valid specifiers are as follows (case-insensitive):

    - ``"Linux"``
    - ``"Windows"``
    - ``"macOS"``
    - ``"auto"``: automatically detect the execution platform
    - ``"POSIX"``: POSIX-compliant systems (Linux, macOS, etc.)
    - ``"universal"``/|None|: platform independent. note that absolute paths cannot specify this.

Defaults to |None|.