# Collect all virtual types accessible by `self`
	#
	# This include introduced, redefined, inherited virtual types.
	fun collect_accessible_vts(mainmodule: MModule, filter: nullable ModelFilter): Set[MVirtualTypeProp] do
		var set = new HashSet[MVirtualTypeProp]
		for mproperty in collect_accessible_mproperties(mainmodule, filter) do
			if mproperty isa MVirtualTypeProp then set.add mproperty
		end
		return set
	end