diff --git a/static/js/dict.js b/static/js/dict.js
index 205075814f..f8b5577f02 100644
--- a/static/js/dict.js
+++ b/static/js/dict.js
@@ -1,4 +1,8 @@
 /* Constructs a new Dict object.
+ *
+ * This module primarily exists to support the fold_case option,
+ * because so many string keys in Zulip are case-insensitive (emails,
+ * stream names, topics, etc.).
  *
  * Dict(opt) -> the new Dict will be empty
  *