So, what's the big idea?
Perl projects have all manner of ways of declaring their dependencies. CPAN releases usually include a file called META.yml or META.json listing their dependencies (though Makefile.PL or Build.PL is also supposed to generate a list of dependencies when it runs; this allows the release to dynamically decide on different dependencies based on the machine it's running on). Non-CPAN projects can declare their CPAN dependencies using cpanfile too.
Once the dependencies are declared, this information is used by CPAN clients, by metacpan.org (to show the list of a release's dependencies), by http://deps.cpantesters.org/ and so on.
However, this only works where you want to declare dependencies on CPAN modules, or on a minimum version of Perl itself.