WebView is not a Control subclass and thus does not have a control template. The display area is the Width and Height.
WebView has the characteristic that other UI regions such as controls cannot be rendered on top of the WebView. This is because of how window regions are handled internally, particularly how input events are processed and how the screen draws. If you want to render HTML content and also place other UI elements on top of that HTML content, you should use WebViewBrush as the render area. The WebView still provides the HTML source information, and you reference that WebView through the SourceName property. WebViewBrush does not have this overlay limitation.
If you want to display an interactive WebView that only occasionally has overlapping content (such as a drop-down list or app bar), you can temporarily hide the WebView control when necessary, replacing it with an element using a WebViewBrush fill. Then, when the overlapping content is no longer present, you can display the original WebView again. For more info, see the WebView control sample.
NoteWebView always uses Internet Explorer 10 in document mode. Additionally, WebView does not currently support some HTML5 features including AppCache, IndexedDB, programmatic access to the Clipboard, or geolocation. Furthermore, WebView does not support the ms-appdata scheme, although it does support the ms-appx-web scheme. This enables you to load content files in your project.