CheckBox.TripleState Property (Outlook Forms Script)
Returns or sets a Boolean that determines whether a user can specify, from the user interface, the Null state for a CheckBox. Read/write.
Syntax
expression .TripleState
expression A variable that represents a CheckBox object.
Remarks
True if the control clicks through three states, False if the control only supports two states, True and False (default).
When the TripleState property is True, a user can choose from the values of Null, True, and False. The Null value is displayed as a shaded button.
When TripleState is False, the user can choose either True or False.
A control set to Null does not initiate the Click event.
Regardless of the property setting, the Null value can always be assigned programmatically to a CheckBox, causing that control to appear shaded.