From d714291aa139b5a7b65edd3d1615f19a8027ac0f Mon Sep 17 00:00:00 2001
From: David Baker <dave@matrix.org>
Date: Fri, 8 Sep 2017 13:27:14 +0100
Subject: [PATCH] Re-add doc on scroll state map structure

---
 src/stores/RoomScrollStateStore.js | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/stores/RoomScrollStateStore.js b/src/stores/RoomScrollStateStore.js
index a1d46a29b8..07848283d1 100644
--- a/src/stores/RoomScrollStateStore.js
+++ b/src/stores/RoomScrollStateStore.js
@@ -19,6 +19,19 @@ limitations under the License.
  */
 class RoomScrollStateStore {
     constructor() {
+        // A map from room id to scroll state.
+        //
+        // If there is no special scroll state (ie, we are following the live
+        // timeline), the scroll state is null. Otherwise, it is an object with
+        // the following properties:
+        //
+        //    focussedEvent: the ID of the 'focussed' event. Typically this is
+        //        the last event fully visible in the viewport, though if we
+        //        have done an explicit scroll to an explicit event, it will be
+        //        that event.
+        //
+        //    pixelOffset: the number of pixels the window is scrolled down
+        //        from the focussedEvent.
         this._scrollStateMap = {};
     }