ENVOLTURA Question about the “RTRG” Jack.

ENVOLTURA Question about the “RTRG” Jack. The “Quick Start Guide” states “DECAY RETRIGGER - A trigger signal restarts the Decay phase of the envelope during the sustain phase”..

However, the guide doesn’t specify whether this is a input or output?

I’m assuming, based on the description that this is a trigger input but thought I would ask just to be sure.

Any help is greatly appreciated.