message: add context for roomsublist rendering
diff: @@ -527,6 +527,8 @@ export default class RoomList extends React.PureComponent<IProps, IState> {
  : this.tagAesthetics[orderedTagId];
  if (!aesthetics) throw new Error(`Tag ${orderedTagId} does not have aesthetics`);
  + // The cost of mounting/unmounting this component offsets the cost
  + // of keeping it in the DOM and hiding it when it is not required
  return <RoomSublist
  key={`sublist-${orderedTagId}`}
  tagId={orderedTagId}
  