I can't find an authoritative/comprehensive description of where CPAN installs its files. I assume there must be a set of rules and that it's not as simple as "XYZ directory" because, for example, multiple users on a Linux box can run CPAN even though there's a single Perl installation and it still somehow works. So, what are those rules?

A second part of this question: The documentation for the PERL5LIB environment variable says that it is "A list of directories in which to look for Perl library files before looking in the standard library and the current directory."

I assume that CPAN doesn't install into the standard library location, since presumably that is fixed for a particular Perl version. So maybe CPAN installs into PERL5LIB?

And finally, as I already alluded to, how does CPAN handle the fact that multiple users might be running the same Perl installation? Sorry if that's a separate question but it seems probably related.