# SEE: `sax::XMLReader.feature=`
	fun feature=(name: String, value: Bool) do
		assert feature_recognized: feature_recognized(name)
		if name == feature_namespaces_uri then
			assert legal_state: value or features[feature_namespace_prefixes_uri] else
				sys.stderr.write("At least one of <{feature_namespaces_uri}> or <{feature_namespace_prefixes_uri}> must be true.\n")
			end
		else if name == feature_namespace_prefixes_uri then
			assert legal_state: value or features[feature_namespaces_uri] else
				sys.stderr.write("At least one of <{feature_namespaces_uri}> or <{feature_namespace_prefixes_uri}> must be true.\n")
			end
		end
		features[name] = value
	end