Enaction

-state-based-

States determine the next available event. Actors are set into various states depending on the events they take part in.

Consider the following description:

Enaction simply means stepping through the description to view the behaviour of actors as they take part in the various events. To enact, simply choose Enhanced option from the Enact menu. The first enaction window is:

The enabled event means it is the only available event, and its precondition is has pen, in other words, for student to give pen, they must have it. The teacher's event is disabled, and their initial state explains why.

When the available event is clicked, the next enaction pane is:

and then..

This goes on and on...because it is a state-driven undertaking that can only change if the user alters the states.

See how to alter states on respective help trails.