I would like to say thanks to Microsoft for providing access to some of  the resources in the local machine.
I can call it as "Sandbox Barrier". It's just a relax to the barrier. Still, we 
do not have full control over the local machine resources.
What is elevated trust mode?
We got this relaxation due to elevated trust mode. This mode enables some features like
- Clipboard Access
 
 Elevated trust mode removes the prompt for permissions to access the clip board.
 
- HTML Hosting
 
 Display HTML content in the web browser control.
 
- Removal of Cross Domain Restrictions
 
 Our application can interact with any domain bypassing the normal security 
	check that required the ClientAccessPolicy.xml or CrossDomain.xml files.
 
- File Access
 
 This enables us to access some of local machine resources without user 
	initiated interaction that invokes the OpenFileDialog. As I mention above, 
	still we are limited user folders such as "My Documents","My Videos","My 
	Pictures","My musics"and any sub folders.
 
 if (App.Current.IsRunningOutOfBrowser 
	&& Application.Current.HasElevatedPermissions)
 {
 string picturesPath =
	Environment.GetFolderPath(Environment.SpecialFolder.MyPictures);
 string path = picturesPath +
	@"\Aru.jpg";
 StreamReader sr =
	new StreamReader(path);
 
 string line = sr.ReadLine();
 while (line != null)
 {
 line = sr.ReadLine();
 }
 sr.Close();
 }
 
- Notification Window
 
 The Notification Window is only available in Out-of-Browser (OOB) mode. You 
	can take advantage of this feature to display confirmation of user's actions 
	("Product saved"), application status ("Application updated, please 
	restart") or warn the user that data were refreshed while he is working on 
	another application.
 
- COM Interoperability
 
 Direct access to COM enabled applications installed on the clients machine
Configure application to run in 
ELEVATED-TRUST-MODE
 
- Create a Silverlight 4 application. Right 
	click on the silverlight application, and select properties.
 
 ![SilApp1.jpg]() 
 
- Select "Enable running application out of 
	browser" check box as shown in figure.
- Once you select the checkbox, you are able 
	to set OOB settings as given bellow.
 
 ![SilApp2.jpg]() 
 
In this OOB settings, select "Require elevated 
trust when running outside the browser".
Now, whenever you install the application, then there will be warning popup.
![SilApp3.jpg]()
We can customize this popup message using digitally signed XAP.