diff --git a/files/en-us/learn/html/multimedia_and_embedding/other_embedding_technologies/index.md b/files/en-us/learn/html/multimedia_and_embedding/other_embedding_technologies/index.md
index 26ccc828be58942..b19543e46759cf4 100644
--- a/files/en-us/learn/html/multimedia_and_embedding/other_embedding_technologies/index.md
+++ b/files/en-us/learn/html/multimedia_and_embedding/other_embedding_technologies/index.md
@@ -123,10 +123,10 @@ body {
 ```
 
 ```js hidden
-const textarea = document.getElementById('code');
-const reset = document.getElementById('reset');
-const solution = document.getElementById('solution');
-const output = document.querySelector('.output');
+const textarea = document.getElementById("code");
+const reset = document.getElementById("reset");
+const solution = document.getElementById("solution");
+const output = document.querySelector(".output");
 let code = textarea.value;
 let userEntry = textarea.value;
 
@@ -134,38 +134,39 @@ function updateCode() {
   output.innerHTML = textarea.value;
 }
 
-reset.addEventListener('click', function() {
+reset.addEventListener("click", function () {
   textarea.value = code;
   userEntry = textarea.value;
   solutionEntry = htmlSolution;
-  solution.value = 'Show solution';
+  solution.value = "Show solution";
   updateCode();
 });
 
-solution.addEventListener('click', function() {
-  if (solution.value === 'Show solution') {
+solution.addEventListener("click", function () {
+  if (solution.value === "Show solution") {
     textarea.value = solutionEntry;
-    solution.value = 'Hide solution';
+    solution.value = "Hide solution";
   } else {
     textarea.value = userEntry;
-    solution.value = 'Show solution';
+    solution.value = "Show solution";
   }
   updateCode();
 });
 
-const htmlSolution = '\n\n';
+const htmlSolution =
+  '\n\n';
 let solutionEntry = htmlSolution;
 
-textarea.addEventListener('input', updateCode);
-window.addEventListener('load', updateCode);
+textarea.addEventListener("input", updateCode);
+window.addEventListener("load", updateCode);
 
 // stop tab key tabbing out of textarea and
 // make it write a tab at the caret position instead
 
-textarea.onkeydown = function(e){
+textarea.onkeydown = function (e) {
   if (e.keyCode === 9) {
     e.preventDefault();
-    insertAtCaret('\t');
+    insertAtCaret("\t");
   }
 
   if (e.keyCode === 27) {
@@ -178,7 +179,10 @@ function insertAtCaret(text) {
   let caretPos = textarea.selectionStart;
 
   const front = textarea.value.substring(0, caretPos);
-  const back = textarea.value.substring(textarea.selectionEnd, textarea.value.length);
+  const back = textarea.value.substring(
+    textarea.selectionEnd,
+    textarea.value.length
+  );
   textarea.value = front + text + back;
   caretPos += text.length;
   textarea.selectionStart = caretPos;
@@ -189,10 +193,10 @@ function insertAtCaret(text) {
 
 // Update the saved userCode every time the user updates the text area code
 
-textarea.onkeyup = function(){
+textarea.onkeyup = function () {
   // We only want to save the state when the user code is being shown,
   // not the solution, so that solution is not saved over the user code
-  if (solution.value === 'Show solution') {
+  if (solution.value === "Show solution") {
     userEntry = textarea.value;
   } else {
     solutionEntry = textarea.value;
@@ -206,9 +210,11 @@ textarea.onkeyup = function(){
 
 ## iframes in detail
 
-So, that was easy and fun, right? {{htmlelement("iframe")}} elements are designed to allow you to embed other web documents into the current document. This is great for incorporating third-party content into your website that you might not have direct control over and don't want to have to implement your own version of — such as video from online video providers, commenting systems like [Disqus](https://disqus.com/), maps from online map providers, advertising banners, etc. The live editable examples you've been using through this course are implemented using `<iframe>`s.
+So, that was easy and fun, right? {{htmlelement("iframe")}} elements are designed to allow you to embed other web documents into the current document. This is great for incorporating third-party content into your website that you might not have direct control over and don't want to have to implement your own version of — such as video from online video providers, commenting systems like [Disqus](https://disqus.com/), maps from online map providers, advertising banners, etc. Even the live editable examples you've been using through this course are implemented using `<iframe>`s.
 
-There are some serious [Security concerns](#security_concerns) to consider with `<iframe>`s, as we'll discuss below, but this doesn't mean that you shouldn't use them in your websites — it just requires some knowledge and careful thinking. Let's explore the code in a bit more detail. Say you wanted to include the MDN glossary on one of your web pages — you could try something like this:
+Before diving into using `<iframe>` elements, there are some security concerns to be aware of.
+Say you wanted to include the MDN glossary on one of your web pages using the {{htmlelement("iframe")}} element, you might try something like the next code example.
+If you were to do add the code below into one of your pages, you might be surprised to see an error message instead of the glossary page:
 
 ```html
 <head>
@@ -234,7 +240,15 @@ There are some serious [Security concerns](#security_concerns) to consider with
 </body>
 ```
 
-This example includes the basic essentials needed to use an `<iframe>`:
+If you have a look at your browser's console, you'll see an error message like the following:
+
+```
+Refused to display 'https://developer.mozilla.org/' in a frame because it set 'X-Frame-Options' to 'deny'.
+```
+
+The [Security](#security_concerns) section below goes into more detail about why you see this error, but first, let's have a look at what our code is doing.
+
+The example includes the bare essentials needed to use an `<iframe>`:
 
 - [`border: none`](/en-US/docs/Web/CSS/border)
   - : If used, the `<iframe>` is displayed without a surrounding border. Otherwise, by default, browsers display the `<iframe>` with a surrounding border (which is generally undesirable).
@@ -284,7 +298,7 @@ HTTPS-enabling your site requires a special security certificate to be installed
 
 You want to give attackers as little power as you can to do bad things on your website, therefore you should give embedded content _only the permissions needed for doing its job._ Of course, this applies to your own content, too. A container for code where it can be used appropriately — or for testing — but can't cause any harm to the rest of the codebase (either accidental or malicious) is called a [sandbox](<https://en.wikipedia.org/wiki/Sandbox_(computer_security)>).
 
-Unsandboxed content can do way too much (executing JavaScript, submitting forms, popup windows, etc.) By default, you should impose all available restrictions by using the `sandbox` attribute with no parameters, as shown in our previous example.
+Content that's not sandboxed may be able to execute JavaScript, submit forms, trigger popup windows, etc. By default, you should impose all available restrictions by using the `sandbox` attribute with no parameters, as shown in our previous example.
 
 If absolutely required, you can add permissions back one by one (inside the `sandbox=""` attribute value) — see the {{htmlattrxref('sandbox','iframe')}} reference entry for all the available options. One important note is that you should _never_ add both `allow-scripts` and `allow-same-origin` to your `sandbox` attribute — in that case, the embedded content could bypass the [Same-origin policy](/en-US/docs/Glossary/Same-origin_policy) that stops sites from executing scripts, and use JavaScript to turn off sandboxing altogether.