diff --git a/Overlay-image-configuration.md b/Overlay-image-configuration.md
index ae072ca..d4b4a8f 100644
--- a/Overlay-image-configuration.md
+++ b/Overlay-image-configuration.md
@@ -19,9 +19,9 @@ The config file describes:
   - Which image should be shown over the input descriptors individually (optional).
   - Where on the screen the entire overlay should be displayed.
 
-### Full-screen overlay images
+### Overlay images
 
-First we configure how many overlays we use. Every overlay can have one full-screen overlay, but is optional. The full-screen overlay is supported for compatibility with older format.
+First we configure how many overlays we use. Every overlay can have one overlay which fills the entire rectangle (`overlay%u_rect`), but is optional. The full-rect overlay is supported for compatibility with older format. It is less flexible than per-button overlays and is discouraged.
 
     overlays = 2
     overlay0_overlay = overlay_img0.png # Optional