The GroupByAreaBase keeps track of its expanded and collapsed state and exposes this property that styles can trigger of off to collapse the elements in the style's Template. The default style for the GroupByAreaBase provides contains a Template that exposes a UI for expanding and collapsing the control.
Target Platforms: Windows 10, Windows 8.1, Windows 8, Windows 7, Windows Server 2012, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2