code: func (e *Engine) handleOverride(o seesaw.Override) {
  	e.overrides[o.Target()] = o
  	e.distributeOverride(o)
  	if o.State() == seesaw.OverrideDefault {
  		delete(e.overrides, o.Target())
  	}
  }
docs: // handleOverride handles an incoming Override.