diff --git a/src/components/main/constellation.rs b/src/components/main/constellation.rs
index c0f28d642e2..a6f1b6f9a40 100644
--- a/src/components/main/constellation.rs
+++ b/src/components/main/constellation.rs
@@ -64,6 +64,8 @@ impl Clone for FrameTree {
 
 struct ChildFrameTree {
     frame_tree: @mut FrameTree,
+    /// Clipping rect representing the size and position, in page coordinates, of the visible
+    /// region of the child frame relative to the parent.
     rect: Option<Rect<f32>>,
 }