diff --git a/server/display-channel-private.h b/server/display-channel-private.h
index afb28b60..a727ddb6 100644
--- a/server/display-channel-private.h
+++ b/server/display-channel-private.h
@@ -41,7 +41,11 @@ struct DisplayChannelPrivate
     int enable_jpeg;
     int enable_zlib_glz_wrap;
 
-    Ring current_list; // of TreeItem
+    /* A ring of pending drawables for this DisplayChannel, regardless of which
+     * surface they're associated with. This list is mainly used to flush older
+     * drawables when we need to make room for new drawables.  The ring is
+     * maintained in order of age, the tail being the oldest drawable */
+    Ring current_list;
 
     uint32_t drawable_count;
     _Drawable drawables[NUM_DRAWABLES];
diff --git a/server/display-channel.h b/server/display-channel.h
index 497f9110..3d4accf1 100644
--- a/server/display-channel.h
+++ b/server/display-channel.h
@@ -162,7 +162,14 @@ typedef struct DrawContext {
 
 typedef struct RedSurface {
     uint32_t refs;
+    /* A Ring representing a hierarchical tree structure. This tree includes
+     * DrawItems, Containers, and Shadows. It is used to efficiently determine
+     * which drawables overlap, and to exclude regions of drawables that are
+     * obscured by other drawables */
     Ring current;
+    /* A ring of pending Drawables associated with this surface. This ring is
+     * actually used for drawing. The ring is maintained in order of age, the
+     * tail being the oldest drawable. */
     Ring current_list;
     DrawContext context;