Checking the file libraries/import.php I'm a question regarding the use of constants IS_WIN, IS_MAC, IS_UNIX.

Somewhere in the CMS are used?

Moreover libraries/joomla/filesystem/path.php file defines constants: JPATH_ISWIN and JPATH_ISMAC on lines 13, 16 respectively.

The file ./libraries/joomla/application/application.php define function 'isWinOS'

The object JFTP in its constructor sets the variable OS.

All these files make use of the form:

<?php
substr(PHP_OS, 0, 3)

to determine the operating system.

the external libraries for example: phpmailer and geshi also make use of this form.

IMHO is necessary to define these variables.

However appear in the documentation. https://github.com/joomla/joomla-platform/blob/staging/docs/manual/en-US/chapters/introduction.xml#L41

Personally I consider that:

1. • These constants should not exist.
2. • Or if the file 'iasf.php' is loaded before the other files, then you should make use of these constants.

Personally I think it's the first best solution(educes the learning curve of the framework).

P. S. I would like to help review this detail.