adding backStackEntry example, including missing import md file text field (#5319)

tests/app/ui/frame/frame.md

@@ -20,3 +20,33 @@ To perform navigation, you will need a reference to the topmost frame of the app
 
 ### Navigating Back
 {%snippet frame-back%}
+
+### Back Navigation with BackstackEntry
+Using the `BackstackEntry` allows us to navigate back to a specific page.
+
+```XML
+<Page xmlns="http://schemas.nativescript.org/tns.xsd" navigatingTo="navigatingTo" class="page">
+
+    <Page.actionBar>
+        <ActionBar title="Page 5" icon="" class="action-bar">
+        </ActionBar>
+    </Page.actionBar>
+
+    <StackLayout class="p-20">
+        <Label text="Page 5" class="h1 text-center"/>
+        <Button text="back to the first page" tap="onTap" class="btn btn-primary btn-active"/>
+    </StackLayout>
+</Page>
+```
+```TypeScript
+import {BackstackEntry, Frame} from "ui/frame"
+
+export function backNavigation(args){
+    const backstackEntryFirstPage = args.object.page.frame.backStack[0];
+    const frame = args.object.page.frame;
+    frame.goBack(backstackEntryFirstPage);
+}
+```
+With the help of the Frame we access the page's BackstackEntry by providing the the sequence number - `backStack[<page number>]`. In the example above we will navigate back to the initial page and to do that we need to take the first BackstackEntry as follow: `topmost().backStack[0]`
+
+> NB: We start counting the pages from 0. If we need to take the entry for the first page we need to take the it while using the 0 index, for the second 1 index, etc.

tests/app/ui/text-field/text-field-tests.ts

@@ -16,11 +16,11 @@ import { Span } from "tns-core-modules/text/span";
 import { TextField } from "tns-core-modules/ui/text-field";
 // << require-textfield
 // Other frequently used modules when working with buttons include:
-
+// >> require-observable-binding-options-textfield
 import { BindingOptions } from "tns-core-modules/ui/core/bindable";
-// >> require-observable-textfield
+
 import { Observable } from "tns-core-modules/data/observable";
-// << require-observable-textfield
+// << require-observable-binding-options-textfield
 
 // ### Binding two TextFields text property to observable view-model property.
 // >> binding-text-property-textfield

tests/app/ui/text-field/text-field.md

@@ -13,7 +13,7 @@ Using a TextField requires the text-field module.
 {%raw%}<TextField text="{{ someProperty }}" />
 <TextField text="{{ someProperty }}" />{%endraw%}
 ```
-{%snippet binding-text-property-textfield%}
+{%snippet require-observable-binding-options-textfield%}
 ## Creating a TextField
 {%snippet creating-textfield%}
 ### Setting the text of a TextField