A character string containing the expanded file specification
    or the field you specify. If you do not provide a complete file
    specification for the filespec argument, the F$PARSE function
    supplies defaults in the return string.

    In most cases, the F$PARSE function returns a null string ("")
    if an error is detected during the parse. For example, a null
    string is returned if the file specification has incorrect
    syntax or if a disk or directory does not exist, making the file
    specification logically incorrect. However, when you specify a
    field name or the SYNTAX_ONLY parse type, F$PARSE returns the
    appropriate information.