docs: describe how order numbers work

docs/en/UI/Angular/Modifying-the-Menu.md

@@ -239,7 +239,7 @@ export class AppComponent {
         id: 'SignOutIcon',
         html: '<i class="fas fa-sign-out-alt fa-lg text-white m-2"><i>',
         action: () => console.log('Clicked the sign out icon'),
-        order: 102, // puts as last element
+        order: 101, // puts as last element
       },
     ]);
   }
@@ -250,6 +250,8 @@ This inserts a search input and a sign out icon to the menu. The final UI looks
 
 ![navigation-menu-search-input](./images/navigation-menu-search-input.png)
 
+> The default elements have an order of `100`. If you want to place a custom element before the defaults, assign an order number up to `99`. If you want to place a custom element after the defaults, assign orders starting from `101`. Finally, if you must place an item between the defaults, patch the default element orders as described below. A warning though: We may add another default element in the future and it too will have an order number of `100`.
+
 ## How to Patch or Remove an Right Part Element
 
 The `patchItem` method of `NavItemsService` finds an element by its `id` property and replaces its configuration with the new configuration passed as the second parameter. Similarly, `removeItem` method finds an element and removes it.