When multiple XTEXT controls are in simultaneous use, specifies which one (range is 0 through 4) to use for this call. If opcode = TXOP_CREATE, you can set TXC.CTLNO to –1 to have XTEXT automatically assign the next available control number. If the control is modeless, you will need to save the returned TXC.CTLNO value for referencing it in subsequent calls. If you use only one XTEXT control at a time, you can just set this to 0 and ignore it.