message: Add comment for StickyContainer extension
diff: @@ -117,7 +117,11 @@ export default class ScrollPanel extends StickyContainer {
  debuglog("Scroll event: offset now:", sn.scrollTop,
  "_lastSetScroll:", this._lastSetScroll);
  + // Set the node and notify subscribers of the StickContainer
  + // By extending StickyContainer, we can set the scroll node to be that of the
  + // ScrolPanel to allow any `<Sticky>` children to be sticky, namely DateSeparators.
  this.node = sn;
  + // Update subscribers - arbitrarily nested `<Sticky>` children
  this.notifySubscribers(ev);
  // Sometimes we see attempts to write to scrollTop essentially being
  