GHRD Max10 - Where is ADC_DEFAULT_SYSFS defined

A bit of a beginners question this one.
I’m using the GHRD on a Max10 Development kit and would like to try modifying a few things to find my feet.
The script which is provided sets a constant

readonly ADC_DEFAULT_SYSFS="/sys/bus/iio/devices/iio:device0/in_voltage0_adc1-ch7_raw"

I haven’t yet been able to work out where in_voltage0_adc1-ch7_raw is defined so I could ,say, add some additional channels. The step beyond that would be to define a memory mapped location to write to.

Any help will be gratefully received