diff --git a/wayland.h b/wayland.h
index 4e5c62ba..28145923 100644
--- a/wayland.h
+++ b/wayland.h
@@ -82,6 +82,11 @@ struct wl_primary {
     uint32_t serial;
 };
 
+/* I'd prefer to position the CSD sub-surfaces outside the main
+ * surface. Unfortunately, a lot of compositors doesn't handle this
+ * correctly. When this define is 0, we instead position the CSD
+ * sub-surfaces inside the main surface, and offset the grid content
+ * accordingly. */
 #define FOOT_CSD_OUTSIDE 0
 extern const int csd_border_size;
 extern const int csd_title_size;