By default the summary record's header contains text derived from settings of FieldLayout's SummaryDescriptionMask and SummaryDescriptionMaskInGroupBy properties. You can use SummaryRecordHeader property to to specify summary record header's contents on a per record collection basis. Also using this property you can specify contents as any arbitrary value which will be presented using a ContentPresenter.
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