Reference-Set Construction and Destruction

Let R be a reference mapping rule defining a set of references S, then:

1. S is constructed when R is activated, and
2. S is destructed when R is de-activated, but only if:

1. R was defined in the <reference-map> element, or
2. S is not a persistent reference-set.

As with xfMap groups, constructed reference-sets can be pictured as residing in some sort of stack, we call this the r-stack, where the top of the stack houses the most immediate constructed reference-set. A destructed reference-set is removed from the r-stack unless it was specified to be a persistent.