diff --git a/src/compositor.c b/src/compositor.c
index ee47a827..40d8bafd 100644
--- a/src/compositor.c
+++ b/src/compositor.c
@@ -1082,16 +1082,15 @@ weston_surface_update_output_mask(struct weston_surface *es, uint32_t mask)
 	}
 }
 
-
 /** Recalculate which output(s) the surface has views displayed on
  *
  * \param es  The surface to remap to outputs
  *
  * Finds the output that is showing the largest amount of one
  * of the surface's various views.  This output becomes the
- * surface's primary output for vsync and frame event purposes.
+ * surface's primary output for vsync and frame callback purposes.
  *
- * Also notes the primary outputs of all of the surface's views
+ * Also notes all outputs of all of the surface's views
  * in the output_mask for the surface.
  */
 static void
@@ -1136,8 +1135,7 @@ weston_surface_assign_output(struct weston_surface *es)
  *
  * Identifies the set of outputs that the view is visible on,
  * noting them into the output_mask.  The output that the view
- * is most visible on is set as the view's primary output for
- * vsync and frame event purposes.
+ * is most visible on is set as the view's primary output.
  *
  * Also does the same for the view's surface.  See
  * weston_surface_assign_output().
diff --git a/src/compositor.h b/src/compositor.h
index 91d1a22d..0bbf4586 100644
--- a/src/compositor.h
+++ b/src/compositor.h
@@ -949,8 +949,9 @@ struct weston_view {
 	} transform;
 
 	/*
-	 * Which output to vsync this surface to.
-	 * Used to determine, whether to send or queue frame events.
+	 * The primary output for this view.
+	 * Used for picking the output for driving internal animations on the
+	 * view, inheriting the primary output for related views in shells, etc.
 	 */
 	struct weston_output *output;
 
@@ -1019,7 +1020,9 @@ struct weston_surface {
 
 	/*
 	 * Which output to vsync this surface to.
-	 * Used to determine, whether to send or queue frame events.
+	 * Used to determine whether to send or queue frame events, and for
+	 * other client-visible syncing/throttling tied to the output
+	 * repaint cycle.
 	 */
 	struct weston_output *output;