The name of the field in the working list that will control a tree item's expanded state. . This is only valid for unlevelled lists and will be ignored if listtype is "levelled"
Default value
Blank. A tree item's expanded state cannot be controlled.
Valid values
The name of the field in the working list that will contain a value of 'True' if an item should be expanded, and 'False' if it should not.
