diff --git a/zephyr/static/js/zephyr.js b/zephyr/static/js/zephyr.js
index cc2a4f9dda..d4735e340f 100644
--- a/zephyr/static/js/zephyr.js
+++ b/zephyr/static/js/zephyr.js
@@ -241,6 +241,7 @@ function add_display_time(message, prev) {
         }
     }
 
+    // NB: timestr is HTML, inserted into the document without escaping.
     if (include_date) {
         message.timestr = time.toString("MMM dd") + "  " +
             time.toString("HH:mm");