private void DrawZones()
        {
            var zones = controller.GetComponentsInChildren <Zone>();

            EditorGUILayout.Space();
            EditorGUI.indentLevel++;

            if (zones.Length > 0)
            {
                for (int i = 0; i < zones.Length; i++)
                {
                    DrawZone(zones[i]);
                }
            }
            else
            {
                EditorGUILayout.LabelField("no zones defined",
                                           EditorToolkit.ErrorLabelStyle()
                                           );
            }

            EditorGUI.indentLevel--;
        }