The GroupWidth and GroupHeight are used to control the size of the CalendarItemGroup instances that the panel creates. Both of these default to double.NaN. When either is left set to NaN, the panel will use a custom hidden CalendarItemGroup to calculate the size required for the groups to replace the NaN value.
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