Add declarations section to archetypes
There is currently no means of easily equating a symbol with a path. If there were,
invariants could be stated economically using the symbols. Such symbols could also be used
for use_node statements.
While this is a nice idea, I don’t think it should be added in the next ADL 2 release.
Maintaining uniqueness is fundamental to the "future-proof" foundation of openEHR.