Maven allows to activate certain build profiles based on the operating system family it runs on, for example:
<profile>
    <activation>
        <os><family>Windows</family></os>
    </activation>
</profile>
There is a number of question around this: what are allowed values for os.family then? Are they case sensitive? Does Linux come across as Unix? Or unix? And so on.
Where can I find information about allowed values – or, at least, where does Maven take these values from? Environment variables?