minor fixes

2-ui/99-ui-misc/01-mutation-observer/article.md

@@ -244,6 +244,7 @@ These methods can be used together, like this:
 
 ```js
 // get a list of unprocessed mutations
+// should be called before disconnecting if you care about possibly unhandled recent mutations
 let mutationRecords = observer.takeRecords();
 
 // stop tracking changes