Returns a Boolean value indicating whether the specified virtual path is relative to the application.
true if virtualPath is relative to the application; otherwise, false.
The virtual path can be just the root operator (the tilde [~]), or it can begin with the root operator. If virtualPath is null, an ArgumentNullException exception is raised. If virtualPath is an empty string (""), the VirtualPathUtility.IsAppRelative(string) method returns false.
"~filename" is not a valid virtual path and returns false for the VirtualPathUtility.IsAppRelative(string) method.