What base does a model have for rigging?

The topic title might not be the best wording, but I can explain it better here.

How does the rigging work? Like, are the models’ animations each individually created, or is there a base skeleton with animations that the model overlays?
I want to port models from a program called ‘MikuMikuDance’ to Garry’s Mod. I want to be able to know how the models are rigged to the skeleton;
Is there a skeleton that the models have to flex and animate to? e.g. if the base skeleton had a waving animation, then all models that had the skeleton like the base one would wave when animation of waving was played.

If you still don’t understand what I am talking about, feel free to ask for clarification.

[SOLVED] http://facepunch.com/threads/719491 gave me the info I needed. :stuck_out_tongue: Admins, please lock this topic or delete it.

Short answer - no.

Longer answer - yes and no.

Essentially you can use any skeleton for animations, but the majority of people who include animations to models tend to use the valve skeleton because they can easily include most of the valve anims.

Ok. Thank you.