THPDFXFAInstanceAction Type
THPDFXFAInstanceAction is the callback assigned to THotPDF.OnXFAInstanceAction
THPDFXFAInstanceActionKind identifies xiaAdd and xiaRemove requests
xiaAdd passes the requested count, while xiaRemove passes the zero-based instance index; return True and set AResultingCount only after the host model accepts the operation
The engine validates names, arguments, item limits, and the aggregate operation budget before invoking the callback; JavaScript requests are queued until script evaluation succeeds