I don't have an example here.. but as far as I remember you define the swimlanes at process definition level and after that you can use an expression to set the property assignee to that swimlane.
In the BPMN file you should be able to see something like
<potentialOwner>
<resourceAssignmentExpression>
<formalExpression>{swimlanename}</formalExpression>
</resourceAssignmentExpression>
</potentialOwner>
Greetings.