Add a passing modal example

Author: tombrunet

_rules/focusable-no-keyboard-trap-standard-nav-a1b64e.md

@@ -79,6 +79,54 @@ This element is made [focusable][] by the `tabindex` attribute, even if it is no
 <div tabindex="-1">Text</div>
 ```
 
+#### Passed Example 4
+
+While the elements with id "sentinelBefore" and "sentinelAfter" contain focus to the contents of the div with name "Sample Modal", focus is not trapped since the user can
+use [standard keyboard navigation](#standard-keyboard-navigation) using the Escape key or by activating the "Close button" to dismiss the modal
+
+```html
+<div>Main page content with <a href="#">some link</a></div>
+<div aria-hidden="true">
+	<a href="#" id="sentinelBefore" style="position:absolute; top:-999em"
+		>Upon receiving focus, this focus sentinel should wrap focus to the bottom of the modal</a
+	>
+</div>
+<div
+	id="sampleModal"
+	role="dialog"
+	aria-label="Sample Modal"
+	aria-modal="true"
+	style="border: solid black 1px; padding: 1rem;"
+>
+	<label>First and last name <input id="dialogFirst"/></label><br />
+	<button id="closeButton">Close button</button>
+</div>
+<div aria-hidden="true">
+	<a href="#" id="sentinelAfter" style="position:absolute; top:-999em"
+		>Upon receiving focus, this focus sentinel should wrap focus to the top of the modal</a
+	>
+</div>
+<script>
+  window.addEventListener('load', () => {
+    document.getElementById('dialogFirst').focus();
+  })
+	document.getElementById('sentinelBefore').addEventListener('focus', () => {
+		document.getElementById('closeButton').focus()
+	})
+	document.getElementById('sentinelAfter').addEventListener('focus', () => {
+		document.getElementById('dialogFirst').focus()
+	})
+	document.getElementById('closeButton').addEventListener('click', () => {
+		document.getElementById('sampleModal').style.display = 'none'
+	})
+  document.getElementById('sampleModal').addEventListener('keydown', (evt) => {
+    if (evt.key === "Escape") {
+      document.getElementById('sampleModal').style.display = 'none';    
+    }
+  })
+</script>
+```
+
 ### Failed
 
 #### Failed Example 1