diff --git a/2-ui/99-ui-misc/01-mutation-observer/article.md b/2-ui/99-ui-misc/01-mutation-observer/article.md
index 6a458fa0..a1602f33 100644
--- a/2-ui/99-ui-misc/01-mutation-observer/article.md
+++ b/2-ui/99-ui-misc/01-mutation-observer/article.md
@@ -1,7 +1,7 @@
 
 # Mutation observer
 
-`MutationObserver` is a built-in object that observes a DOM element and fires a callback in case of changes.
+`MutationObserver` is a built-in object that observes a DOM element and fires a callback if there are changes.
 
 We'll first take a look at the syntax, and then explore a real-world use case, to see where such thing may be useful.
 
@@ -128,16 +128,16 @@ Such snippet in an HTML markup looks like this:
 ...
 ```
 
-Also we'll use a JavaScript highlighting library on our site, e.g. [Prism.js](https://prismjs.com/). A call to `Prism.highlightElem(pre)` examines the contents of such `pre` elements and adds into them special tags and styles for colored syntax highlighting, similar to what you see in examples here, at this page.
+Also we'll use a JavaScript highlighting library on our site, e.g. [Prism.js](https://prismjs.com/). A call to `Prism.highlightElem(pre)` examines the contents of such `pre` elements and adds into them special tags and styles for colored syntax highlighting, similar to what you see in examples here, on this page.
 
-When exactly to run that highlighting method? We can do it on `DOMContentLoaded` event, or at the bottom of the page. At that moment we have our DOM ready, can search for elements `pre[class*="language"]` and call `Prism.highlightElem` on them:
+When exactly should we run that highlighting method? We can do it on `DOMContentLoaded` event, or at the bottom of the page. At that moment we have our DOM ready, we can search for elements `pre[class*="language"]` and call `Prism.highlightElem` on them:
 
 ```js
 // highlight all code snippets on the page
 document.querySelectorAll('pre[class*="language"]').forEach(Prism.highlightElem);
 ```
 
-Everything's simple so far, right? There are `<pre>` code snippets in HTML, we highlight them.
+Everything's simple so far, right? Where there are `<pre>` code snippets in HTML, we highlight them.
 
 Now let's go on. Let's say we're going to dynamically fetch materials from a server. We'll study methods for that [later in the tutorial](info:fetch). For now it only matters that we fetch an HTML article from a webserver and display it on demand:
 
@@ -162,13 +162,13 @@ snippets.forEach(Prism.highlightElem);
 */!*
 ```
 
-...But imagine, we have many places in the code where we load contents: articles, quizzes, forum posts. Do we need to put the highlighting call everywhere? That's not very convenient, and also easy to forget.
+...But imagine, we have many places in the code where we load content: articles, quizzes, forum posts. Do we need to put the highlighting call everywhere? That's not very convenient, and also easy to forget.
 
-And what if the content is loaded by a third-party module? E.g. we have a forum written by someone else, that loads contents dynamically, and we'd like to add syntax highlighting to it. No one likes to patch third-party scripts.
+And what if the content is loaded by a third-party module? E.g. we have a forum written by someone else, that loads content dynamically, and we'd like to add syntax highlighting to it. No one likes patching third-party scripts.
 
 Luckily, there's another option.
 
-We can use `MutationObserver` to automatically detect when code snippets are inserted in the page and highlight them.
+We can use `MutationObserver` to automatically detect when code snippets are inserted into the page and highlight them.
 
 So we'll handle the highlighting functionality in one place, relieving us from the need to integrate it.
 
@@ -236,9 +236,9 @@ There's a method to stop observing the node:
 
 - `observer.disconnect()` -- stops the observation.
 
-When we stop the observing, it might be possible that some changes were not processed by the observer yet.
+When we stop the observing, it might be possible that some changes were not yet processed by the observer.
 
-- `observer.takeRecords()` -- gets a list of unprocessed mutation records, those that happened, but the callback did not handle them.
+- `observer.takeRecords()` -- gets a list of unprocessed mutation records, those that happened, but the callback has not handled them.
 
 These methods can be used together, like this:
 
@@ -252,14 +252,14 @@ let mutationRecords = observer.takeRecords();
 ```
 
 ```smart header="Garbage collection interaction"
-Observers use weak references to nodes internally. That is: if a node is removed from DOM, and becomes unreachable, then it becomes garbage collected.
+Observers use weak references to nodes internally. That is: if a node is removed from the DOM, and becomes unreachable, then it can be garbage collected.
 
 The mere fact that a DOM node is observed doesn't prevent the garbage collection.
 ```
 
 ## Summary  
 
-`MutationObserver` can react on changes in DOM: attributes, added/removed elements, text content.
+`MutationObserver` can react to changes in DOM: attributes, added/removed elements, text content.
 
 We can use it to track changes introduced by other parts of our code, as well as to integrate with third-party scripts.