In DCharts, is regarded as a special event. It is comparable to the (timeout) in David Harel's STATEMATE statecharts. Though it appears in the event part of a transition, it is not really an event but a schedule request. It also has a special syntax where is the schedule time (in seconds) as a parameter. For example, if is , the transition with such an will be triggered after 10 seconds in real-time (if the model stays in its state).
The meaning of ``after 10 seconds'' must be clarified. is the source state of transition . When the model changes to or any substate of from the outside, transitions from with events are collected. Their scheduled times are evaluated. The is usually a constant float number. However, a specific implementation may allow to use expressions to specify . Those expressions are evaluated at run-time. Each of such transitions will be triggered after the resulting number of seconds, counting from the moment when the of all those transitions are evaluated. Of course, there might be slight difference in the timing of those transitions. The accuracy is implementation-dependent.
When the model leaves state , the scheduled transitions from or its substates that have not been triggered yet, are canceled. In particular, if Harel's algorithm for firing a transition (section 2.3.1) is used, scheduled transitions from are re-scheduled when a self-loop on is triggered (because is the parent of ); if the alternate algorithm (section 2.3.2) is used, they are not re-scheduled or canceled (because is itself).