I'm getting a bit lost in the Bermuda triangle of attributes, attribute
types, and properties in the Bro type system. If somebody who has
managed to escape could say a few words about the difference in
semantics between MutableVal's properties vs attributes, the different
purposes of the attr member in IDs, the attribute member in Vals, and
the attributes_type member Type.h, that would be much appreciated. Do I
understand correctly that the attributes_type member is only relevant
when somebody uses the &attr attribute?