Location of files that determine caravan animals

[Ekksu]

Heya! Getting into modding, and I'm trying to add more animals as caravan/pack animals. I've been sorting through the .xml files, and I haven't been able to find it anywhere in any of the defs where I figured it'd be. Where is it? Or is it in the .dll files? I think I might've missed it, but I'm not sure.