Status: IN
Visitor's dual class hierarchy architecture (orthogonal element and visitor hierarchies) is a primary structural mechanism that supports OCP axis inversion: the standard OCP axis (add new types) relies on a single hierarchy, while inverting it (add new operations) benefits from a second orthogonal hierarchy to house new operations independently of the element hierarchy — the dual hierarchy provides the structural foundation for bidirectional extensibility, though the antecedents establish this as the mechanism enabling structural independence and explicit axis tradeoff rather than demonstrating it is the only possible approach.
The dual hierarchy is the structural prerequisite that makes double-dispatch OCP inversion possible, not just a convenience
Depends on (SL): visitor-dual-hierarchy-enables-structural-independence, visitor-dispatch-implements-ocp-inversion