The timeline editor tool is depicted in Figure 1 . These are non-deterministic events, typically input from users or external entities. These are events that are required in response to previous events and constraints that have been detected. It is an error if required events are not detected. In addition to events, there are also constraints.
Constraints persist over certain intervals of the property.
A constraint, denoted as a horizontal line, starts at one mark, and ends at the same or another mark. A constraint may or may not include the mark to which its end point is assigned. Marks are the blue, vertical lines on which events are placed. Each mark can only have one event. Marks are not clock ticks, but rather are event ticks.