A new permission that represents the union of the current permission and the specified permission.
The result of a call to UIPermission.Union(System.Security.IPermission) is a permission that represents all the operations represented by the current permission as well as all the operations represented by the specified permission. Specifically, it represents the most permissive values of System.Security.Permissions.UIPermissionWindow and System.Security.Permissions.UIPermissionClipboard from those in the current permission and the specified permission.