diff --git a/examples/ch02/07-key-codes.html b/examples/ch02/07-key-codes.html
index e094d5b..633a053 100644
--- a/examples/ch02/07-key-codes.html
+++ b/examples/ch02/07-key-codes.html
@@ -12,6 +12,8 @@
     <aside>Open debugging console in web browser and press arrow key.</aside>
     
     <script>
+      // for submitting form with "Enter" button the keycode is 13.
+      // to check keycode for the button you want refer https://keycode.info/
     window.onload = function () {
 
       function onKeyboardEvent (event) {