A new parameter named EnableExpressions has been added to the PTypeToggle widget. For compatibility with existing code, EnableExpressions is the last parameter and is optional.
If EnableExpressions is set to 1, a checkbox will be shown that toggles display of the ExpressionEdit widget, which in turn allows users to enter an expression. EnableExpressions defaults to 0, but if the value controlled by the PTypeToggle is already an expression, the expressions checkbox will be displayed regardless.