I’ve read the reform manual 2nd revision, and my keyboard doesn’t match the described layout at all; I’ve found the ones I care about (volume, brightness) as SUPER but not the Fkeys described. The mappings are fine and not a problem.
But the HYPER key seems to do literally nothing. It doesnt seem to have a scan code, according to the evtest program (likewise circle key).
I’d like to remap HYPER to be CONTROL.
Am I just looking at the wrong docs?
iirc, the default reform keyboard firmware maps the hyper key to be a modifier that switches “layers” (changes the scan codes sent by other keys). To remap that key you will need to compile and flash a new firmware to the keyboard.
HYPER is modifier
I assumed that also; I methodically tried HYPER held, pressed other key, vs. not. For most keys HYPER did not affect the scan code; for HYPER-F1 and -F2 returned no code, whereas HYPER-xxx (where xxx is every other key tried) returned the scan code for that key with HYPER not pressed.
Does evtest normally grab media and brightness keys? A quick search shows some behaviors where those might be going through a different event channel or it will fail to capture media keys.
You may also be in the 2nd layer, its a toggled state from hyper+circle, that would explain why you might not see hyper+arrows doing page up/down.
In either case, to your original question, hyper by itself will not send a scan code, you need a different keyboard firmware to change that behavior.
edit: you are saying the function keys send brightness/audio by default? you are in the 2nd layer for sure then, toggle with hyper+circle.
Yes, evtest does display key codes for SUPER-F1 brightness etc.
OK I wasn’t aware of the layers business. HYPER+CIRCLE does testably toggle some background state; in one, F8 generates a code, 70041 KEY_F8, and with HYPER, no code generated. In the other state, no code generated, HYPER pressed or not.
but this does answer my internal question pretty well – I will not be mapping HYPER to control!
(My fingers are long; some of the default mappings were excruciating. DEL i now shift. I may swap CTRL and SUPER to give my little finger a rest 
)
A few weeks ago a feature was added to the stock firmware that allows to swap Control and Hyper keys: Add option KBD_SWP_CTRL for swapping Ctrl- and Hyper-Keys. (d4211b2c) · Commits · Reform / reform · GitLab
You need to build the firmware with KBD_SWP_CTRL option added. I’ve been using the setup since it made it into the firmware.
Ok that’s great! Thanks. So I’m not the only one. (That left corner is very tight for my hand but the keyboard and especially the keys, are just the best.)