diff --git a/config.h b/config.h
index 14b2947..0f157b3 100644
--- a/config.h
+++ b/config.h
@@ -1,14 +1,18 @@
-/* */
+/* default window dimensions:                            */
 #define WIN_WIDTH  800
 #define WIN_HEIGHT 600
 
-/* */
+/* default color to use for window background:           *
+ *   (see X(7) "COLOR NAMES" section for valid values)   */
 #define BG_COLOR   "#888888"
 
-/* */
+/* default scale mode when loading a new image:          *
+ *   SCALE_DOWN: 100%, but fit large images into window, *
+ *   SCALE_FIT:  fit all images into window,             *
+ *   SCALE_ZOOM: use current zoom level, 100% at startup */
 #define SCALE_MODE SCALE_DOWN
 
-/* */
+/* levels (percent) to use when zooming via '-' and '+': */
 static const float zoom_levels[] = {
 	 12.5,  25.0,  50.0,  75.0,
 	100.0, 150.0, 200.0, 400.0, 800.0