What is the function of the variable "IO_PRESENT" in the script "\ROMFS\px4fmu_common\init.d"?

PX4 Autopilot Configuration & Flight Modes ⚙️
1

part of the script

   set IO_PRESENT no

if [ $USE_IO == yes ]
then
	#
	# Check if PX4IO present and update firmware if needed
	#
	if [ -f /etc/extras/px4io-v2.bin ]
	then
		set IO_FILE /etc/extras/px4io-v2.bin
	else
		set IO_FILE /etc/extras/px4io-v1.bin
	fi

	if px4io checkcrc ${IO_FILE}
	then
		echo "PX4IO CRC OK" >> $LOG_FILE

		set IO_PRESENT yes
	else
		echo "PX4IO Trying to update" >> $LOG_FILE

		tone_alarm MLL32CP8MB

		if px4io start
		then
			# try to safe px4 io so motor outputs dont go crazy
			if px4io safety_on
			then
				# success! no-op
			else
				# px4io did not respond to the safety command
				px4io stop
			fi
		fi

		if px4io forceupdate 14662 ${IO_FILE}
		then
			usleep 500000
			if px4io checkcrc $IO_FILE
			then
				echo "PX4IO CRC OK after updating" >> $LOG_FILE
				tone_alarm MLL8CDE

				set IO_PRESENT yes
			else
				echo "ERROR: PX4IO update failed" >> $LOG_FILE
				tone_alarm $TUNE_ERR
			fi
		else
			echo "ERROR: PX4IO update failed" >> $LOG_FILE
			tone_alarm $TUNE_ERR
		fi
	fi
	unset IO_FILE

	if [ $IO_PRESENT == no ]
	then
		echo "[i] ERROR: PX4IO not found"
		echo "ERROR: PX4IO not found" >> $LOG_FILE
		tone_alarm $TUNE_ERR
	fi
fi
2

seems obvious from the script. Could you be more specific?