Explain how to test if element attached to main DOM

Enelar · Enelar · commit 1b0d12b66409 · 2016-09-03T12:36:10.000+03:00
diff --git a/page/using-jquery-core/faq/how-do-i-test-whether-an-element-exists.md b/page/using-jquery-core/faq/how-do-i-test-whether-an-element-exists.md
@@ -17,3 +17,14 @@ Note that it isn't always necessary to test whether an element exists. The follo
 ```
 $( "#myDiv" ).show();
 ```
+
+If you need to understand if element is present in main DOM tree, or if you're previously stored selector set in variable, use [jQuery.contains](https://api.jquery.com/jQuery.contains/)
+
+```
+var elements = $('#myDiv');
+if ($.contains(document, elements)) {
+  elements.show();
+}
+```
+
+Because modern browsers detaching elements in [DocumentFragment](https://developer.mozilla.org/ru/docs/Web/API/Document/createDocumentFragment), `.length` will always return constant value, even if element already removed from page.
