This is news to me (thanks Pav):
$ make -V VALID_CATEGORIES
accessibility afterstep arabic archivers astro audio benchmarks biology cad chinese comms converters databases deskutils devel docs dns editors elisp emulators finance french ftp games geography german gnome gnustep graphics hamradio haskell hebrew hungarian ipv6 irc japanese java kde kld korean lang linux lisp mail math mbone misc multimedia net net-im net-mgmt net-p2p news palm parallel pear perl5 plan9 polish portuguese ports-mgmt print python ruby rubygems russian scheme science security shells spanish sysutils tcl textproc tk ukrainian vietnamese windowmaker www x11 x11-clocks x11-drivers x11-fm x11-fonts x11-servers x11-themes x11-toolkits x11-wm xfce zope
This produces a canonical list of categories. This includes virtual categories as well.
For my own notes: Creating a New Category.
