Ah yes, I forgot there was a GTK+ UI for deluge (I've usually messed around with the web UI).
I don't get your point about aria2 though. That just confirms what I posted. That doing a package manager search would give your more information than the linked article.
Since when does apt-cache show tags? Mine doesn't, I have
$ apt-cache policy apt | grep Installed
Installed: 1.2.24He's using the `show` parameter which does include tags. However you can't really grep it like he had done because the tags can span multiple lines with indentation rather than line prefixes (ie human readable rather than machine readable).
apt-cache show doesn't show tags for me:
$ apt-cache show aria2 | grep Tag
$ echo $?
1
> * Deluge: no reference that it is a command line program which requires quite a bit of configuring to get a web gui working