Users can only use UIPermissionWindow.SafeTopLevelWindows and UIPermissionWindow.SafeSubWindows for drawing, and can only use user input events for the user interface within those top-level windows and subwindows.
When it runs under UIPermissionWindow.SafeTopLevelWindows permission, your application:
Will show the DNS name or IP address of the Web site from which the application was loaded in its title bar.
Will display Balloon tool-tip when it first displays, informing the user that it is running under a restricted trust level.
Must display its title bar at all times.
Must display window controls on its forms.
Cannot minimize its main window on startup.
Cannot move its windows off-screen.
Must use only rectangular windows, and must include the window frame. Windows Forms will not honor setting System.Windows.Forms.Form.FormBorderStyle to None.
Must have an entry in the Task Bar.
Will have its controls prohibited from accessing the System.Windows.Forms.Control.Parent property. By implication, controls will also be barred from accessing siblings - i.e., other controls at the same level of nesting.
Cannot control focus using the System.Windows.Forms.Control.Focus method.
Will have restricted keyboard input access, so that a form or control can only access keyboard events for itself and its children.
Will have restricted mouse coordinate access, so that a form or control can only read mouse coordinates if the mouse is over its visible area.
Cannot set the System.Windows.Forms.Form.TopMost property.
These restrictions help prevent potentially harmful code from spoofing attacks, such as imitating trusted system dialogs.