ABS on the TV...not the trailer
Some say on the trailer too, as most of the modern trailer brake controllers are PWM'd (pulse width modulated...digital), but unless there is an AMS module on a trailer hydraulic braking system...not likely IMHO
The hysteresis (raise time...AKA slop of that curve/incline) is NOT fast enough to accomplish an ABS braking session
Plus, trailer wiring and the magnets will have too much impedance (flux field build up will take too long and the falling off (turn off) like wise will take too long)
So it just sends voltage to the trailer brakes (all of them) at whatever preset it is at (boost, gain, etc)
Agree...should not happen in the first place if properly sized/setup/etc. Even the OEM's which offer it on their products has a 'recommendation' for that option...and it is to have it properly sized/setup or some such CYA fine print