Some (most?) packages in Debian, have tags. For example:
=# apt-cache show squirrelmail | perl -lne 'print if /^Tag:/.../^\S/'
Tag: implemented-in::php, interface::web, mail::imap, mail::smtp,
mail::user-agent, network::server, protocol::http, protocol::imap,
protocol::smtp, role::program, scope::application, use::browsing,
use::editing, use::searching, use::transmission, use::viewing,
web::TODO, web::application, works-with::mail
Section: web
But, I can't find a way, to list all packages with given tag. Is it possible?