public System.Nullable<bool> AllowCollapsing {get; set;}

'Declaration
 
Public Property AllowCollapsing As System.Nullable(Of Boolean)

Property Value

Target Platforms: Windows 8.1, Windows 8.1, Windows 8, Windows 7, 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

Reference

CustomToolbarModel Class
CustomToolbarModel Members