Calling the workflow module

I'm writing some custom modules for a web application. It would be very handy to call directly into the workflow module to find (for example) all the valid next states for a given user and node, or to make a call that updates the workflow state of a node. I don't want to grub around in the database to get this done, because it's nasty and it would probably break later.

So this might be a n00b question but is there API documentation for the workflow module?

Thanks,
Tom