apt: how to search using package tags?

Question

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?

Answer 1

You probably want to take a look at all the documentation surrounding Debtags. It's... not as simple as you might think. No, I don't know why, either.

Answer 2

use axi-cache from the apt-xapian-index package. you can, for example do axi-cache search --all protocol::smtp. The tab-completion for axi-cache is extremely advanced, so hit tab often. for example, i-cache search --all protocol::smtp <tab><tab> will show you what other tags you might want based on the fact that you already specified the first.