There is no restriction on the number of control links in which a control can participate. However, the control cannot be active in more than one link at a time. For example, a single DR1 Level control could participate in two different control links (Link1 and Link2). But if both Link1 and Link2 are active, the DR1 Level control can be active in only one of the links. How does HAL decide which link governs the DR1 Level control in this situation? The answer? The control link priority.
Halogen places each created control link in a prioritized list. If a control participates in multiple active control links, that control is active only in the control link with the highest priority. Staying with the above example, let's say that Link1 is higher in the priority list than Link2. Link2 is currently active, but then someone activates Link1. What happens to that DR1 Level control? It becomes active in Link1 and is no longer active in Link2.
Even though Priority is set at the link level, it actually governs the individual participants in a link, not the entire link. In the example we just discussed, let's assume there are several other controls participating in Link2 — but not participating in Link1. These other controls remain active in Link2 when Link1 is activated. The following diagram helps illustrate this concept:
(Mouse over the diagram to view it.)