Takes two paths as strings, or a path and a basename as strings. It combines them and returns the result.
(string) Path, filename, or path and filename.
(string) Concatenation of input parameters with a directory separator between them.
The function is not file system aware; it does not check to see if the path of file exists, and does not change the input strings.
The function is OS aware; it assumes the directory separator is \ on Windows and / on other OS.