# Recursively generate node and clusters for a mgroup
	private fun dot_cluster(o: Writer, mgroup: MGroup)
	do
		# Open the cluster, if required
		if mgroup.parent == null then
			# is is a root group, so display the package
			if package_group then
				o.write("subgraph cluster_{mgroup.object_id} \{\nlabel=\"{mgroup.mpackage.name}\\n({mgroup.filepath or else "?"})\"\ncolor=black\nstyle=dotted\n")
			end
		else
			if cluster_group then
				o.write("subgraph cluster_{mgroup.object_id} \{\nlabel=\"{mgroup.name}\"\ncolor=blue\nstyle=dotted\n")
			end
		end

		# outputs the mmodules to show
		for mmodule in mgroup.mmodules do
			if not mmodules.has(mmodule) then continue
			o.write("\t{node_for(mmodule)} [label=\"{mmodule.name}\",color=green]\n")
		end

		# recursively progress on sub-clusters
		for d in mgroup.in_nesting.direct_smallers do
			dot_cluster(o, d)
		end

		# close the cluster if required
		if mgroup.parent == null then
			if package_group then o.write("\}\n")
		else
			if cluster_group then o.write("\}\n")
		end
	end