If AllowToggle is to true then holding down the 'Ctrl' key while clicking on a selectable item will toggle its selection state. The same behavior applies when holding the 'Ctrl' key down and using the keyboard to select/deselect the item.
For example, holding the 'Ctrl' key down and pressing the space bar while focus is within a XamDataGrid (with its FieldLayoutSettings.SelectionTypeRecord set to 'Single') will toggle the selection state of its ActiveRecord assuming there is no ActiveCell.
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