A swimlane is a process role. It is a mechanism to specify that multiple tasks in the process should be done by the same actor. So after the first task instance is created for a given swimlane, the actor should be remembered in the process for all subsequent tasks that are in the same swimlane. A swimlane therefore has one assignment and all tasks that reference a swimlane should not specify an assignment.

When the first task in a given swimlane is created, the AssignmentHandler of the swimlane is called. The Assignable that is passed to the AssignmentHandler will be the SwimlaneInstance. Important to know is that all assignments that are done on the task instances in a given swimlane will propagate to the swimlane instance. This behaviour is implemented as the default because the person that takes a task to fulfilling a certain process role will have the knowledge of that perticular process. So all subsequent assignements of task instances to that swimlane are done automatically to that user.

Swimlane is a terminology borrowed from UML activity diagrams.