We are developing a style guide for workflow diagrams created by our staff.  Two questions about technique:

1.  System elements - We know that this can be used to represent a process that occurs in a system.  The question is whether it is common to put these in a separate swimlane (System swimlane) or whether it is okay to have the system step within a regular user swimlane.  Does the 2nd option break any rules?

2. Off-page reference elements - Can a diagram end with an off-page reference or must it have also an "start/end" element. Is that redundant?