How to add arbitrarily-timed events to a Simulink simulation?

My simulation takes an array of state variables and modifies it according to the effects of a series of events. I would like to implement these events so that they could occur in any order, with any timing, and follow branching paths based on current state(s). What's the best strategy for doing this in Simulink, e.g. function-call vs triggered subsystems, should I write a MATLAB function or is there something pre-made that's suitable, etc.