Where can I find a full list of available preconditions?

I am looking for a precondition to enable me to make attributes mandatory at specific states in a workflow - for example when I resolve a defect I want some fields to be mandatory that were optional when it was raised. I found the precondition for required attributes when saving a work item, but of course this works for all states.

Is there a precondition for what I want to do?
Is there a list of available preconditions I can review?

Jim.