adding mime-types

[Andreas Goesele <Goesele hfph mwn de>]

I would like to add some mime types. The documentation says I should
press the Add button in the Gnome Mime Type Capplet. But as hard as I
try, I can't find such a button. (I can't even find it in the screenshot
in the documentation.)

So, please, can anybody explain me where I can find this Add button, or
- even better - how I can add/edit mime types "by hand" (editing some
configuration file).

Thanks in advance

Andreas Gösele