# Page Visibility IDL tests

    interface Document {
    };

    [TreatNonObjectAsNull]
    callback EventHandlerNonNull = any (Event event);
    typedef EventHandlerNonNull? EventHandler;

    enum VisibilityState { "hidden", "visible", "prerender", "unloaded" };

    partial interface Document {
      readonly attribute boolean hidden;
      readonly attribute VisibilityState visibilityState;
    };