Add markdown documentation for new KeyDownTriggerBehavior

docs/behaviors/KeyDownTriggerBehavior.md

@@ -0,0 +1,46 @@
+---
+title: Key Down Trigger Behavior
+author: XAML-Knight
+description: Add a new behavior that listens to a key press event on the associated UIElement and triggers the set of actions.
+keywords: windows 10, uwp, windows community toolkit, uwp community toolkit, uwp toolkit, textbox, behaviors, interactivity, KeyDownTrigger, key down trigger
+dev_langs:
+  - csharp
+---
+
+# Key Down Trigger Behavior
+
+Add a new behavior that listens to a key press event on the associated UIElement and triggers the set of actions.
+
+> **Platform APIs:** [`KeyDownTriggerBehavior`](/dotnet/api/microsoft.toolkit.uwp.ui.behaviors.keydowntriggerbehavior)
+
+> [!div class="nextstepaction"]
+> [Try it in the sample app](uwpct://Helpers?sample=KeyDownTriggerBehavior)
+
+## Example
+
+In this example setting up the `KeyDownTriggerBehavior` to start the animation:
+
+```xaml
+  <TextBox
+    PlaceholderText="Set the focus to this TextBox and press enter to trigger the animation"
+    Width="500">
+        <interactivity:Interaction.Behaviors>
+            <behaviors:KeyDownTriggerBehavior
+                Key="Enter">
+                <behaviors:StartAnimationAction Animation="{Binding ElementName=MoveAnimation}" />
+            </behaviors:KeyDownTriggerBehavior>
+        </interactivity:Interaction.Behaviors>
+    </TextBox>
+```
+
+## Sample Project
+
+[Key Down Trigger behavior sample page Source](https://github.com/windows-toolkit/WindowsCommunityToolkit/tree/main/Microsoft.Toolkit.Uwp.SampleApp/SamplePages/KeyDownTriggerBehavior). You can [see this in action](uwpct://Helpers?sample=KeyDownTriggerBehavior) in [Windows Community Toolkit Sample App](https://aka.ms/windowstoolkitapp).
+
+## Source Code
+
+- [Key Down Trigger behavior source code](https://github.com/windows-toolkit/WindowsCommunityToolkit/tree/main/Microsoft.Toolkit.Uwp.UI.Behaviors/Keyboard)
+
+## Related Topics
+
+- [XAML Behaviors](https://github.com/microsoft/XamlBehaviors/wiki)

docs/toc.md

@@ -279,6 +279,8 @@
 
 ### [Header Behaviors](behaviors/HeaderBehaviors.md)
 
+### [Key Down Trigger Behavior](behaviors/KeyDownTriggerBehavior.md)
+
 ### [ImageCache](helpers/ImageCache.md)
 
 ### [IncrementalLoadingCollection](helpers/IncrementalLoadingCollection.md)