When you create a Silverlight project using Visual Studio 2008, it creates a default xaml file called "Page.xaml". This is just a dummy start page created by Visual Studio and it does not contain any visible UI elements. The default content of the page.xaml file looks like this:
<Grid x:Name="LayoutRoot" Background="White">
The above code shows a user control and a Grid control. The UserControl is a high level control that holds all other UI elements in a xaml file.
The Grid control is used as a layout panel and it can hold other UI elements. All UI elements in a .xaml control must be placed within a layout panel. There 3 different types of layout panels available in Silverlight 2.0. You will learn more about layout controls in a later chapter.
When you compile your Silverlight Application project, it will compile all .xaml files and various other resources in to a single assembly file. This assembly file will have the extension .xap and will have the same file name as your project name.
To place your Silverlight control in a web page, you must refer to this .xap file in your web page. When the .xap file is referred in a web page, the default .xaml page will be shown. Based on user actions, you may open or close various .xaml files included in your .xap assembly (Silverlight Application project).