diff --git a/packages/studio/src/player/hooks/useTimelinePlayer.ts b/packages/studio/src/player/hooks/useTimelinePlayer.ts
index 5ab8b87e7..4614b3936 100644
--- a/packages/studio/src/player/hooks/useTimelinePlayer.ts
+++ b/packages/studio/src/player/hooks/useTimelinePlayer.ts
@@ -134,6 +134,10 @@ export function useTimelinePlayer() {
       if (win.__timelines) {
         const keys = Object.keys(win.__timelines);
         if (keys.length > 0) {
+          // Resolve the root composition id from the DOM — the outermost
+          // `[data-composition-id]` element is the master. Without this,
+          // Object.keys() order would let a sub-composition's timeline
+          // hijack play/pause/seek and the duration readout.
           const rootId = iframe?.contentDocument
             ?.querySelector("[data-composition-id]")
             ?.getAttribute("data-composition-id");