What does ? mean before a label

[gerrykurz]

Can someone explain what the ? mark means in the following task implementations from the TSN API:

[[combinable]]
void
avb_1722_1_maap_task(otp_ports_t & ?otp_ports,
client interface avb_interface i_avb,
client interface avb_1722_1_control_callbacks i_1722_1_entity,
fl_QSPIPorts & ?qspi_ports,
client interface ethernet_rx_if i_eth_rx,
client interface ethernet_tx_if i_eth_tx,
client interface ethernet_cfg_if i_eth_cfg,
chanend c_ptp)

or

void
gptp_media_clock_server(
server interface media_clock_if media_clock_ctl,
chanend ?ptp_svr,
chanend(& ?buf_ctl)[num_buf_ctl],
unsigned num_buf_ctl,
out buffered port:32 p_fs[],
client interface ethernet_rx_if i_eth_rx,
client interface ethernet_tx_if i_eth_tx,
client interface ethernet_cfg_if i_eth_cfg,
chanend c_ptp[num_ptp],
unsigned num_ptp,
enum ptp_server_type server_type)

[babazaroni]

It means the item is a nullable resource.

Here's a link to nullable resources: https://www.xmos.com/published/how-use- ... s?secure=1

[gerrykurz]

Thanks