diff --git a/src/TabComplete.js b/src/TabComplete.js
index 5b7be7c286..0ec0b77802 100644
--- a/src/TabComplete.js
+++ b/src/TabComplete.js
@@ -48,7 +48,12 @@ class TabComplete {
         this.isFirstWord = false; // true if you tab-complete on the first word
         this.enterTabCompleteTimerId = null;
         this.inPassiveMode = false;
+
+        // Map tracking ordering of the room members.
+        // userId: integer, highest comes first.
         this.memberTabOrder = {};
+
+        // monotonically increasing counter used for tracking ordering of members
         this.memberOrderSeq = 0;
     }
 
diff --git a/src/components/structures/RoomStatusBar.js b/src/components/structures/RoomStatusBar.js
index 4309b1e849..9a0d3dbbdd 100644
--- a/src/components/structures/RoomStatusBar.js
+++ b/src/components/structures/RoomStatusBar.js
@@ -28,7 +28,7 @@ module.exports = React.createClass({
         room: React.PropTypes.object.isRequired,
 
         // a TabComplete object
-        tabComplete: React.PropTypes.object,
+        tabComplete: React.PropTypes.object.isRequired,
 
         // the number of messages which have arrived since we've been scrolled up
         numUnreadMessages: React.PropTypes.number,