Update on.md

snippets/on.md

@@ -7,7 +7,8 @@ Use `EventTarget.addEventListener()` to add an event listener to an element. If
 target specified and then invoke the callback by supplying the correct `this` context.
 Use `options` to pass options to `addEventListener` or omit it to use bubbling by default.
 In order to use this function with `off`, the reference to the custom delegator function
-is returned if the `target` option is specified.
+is returned if the `target` option is specified. Omit `opts` to default to non-delegation 
+behavior and event bubbling.
 
 ```js
 const on = (el, evt, fn, opts = {}) => {