Android - inter-app MIDI

[invisibleagent]

Hi,
I'm using Lemur 5.3.3 on Android, the update details say
"Add support for hardware MIDI devices, inter-app MIDI and MIDI over USB"

So considering Lemur on Android does not support USB MIDI Cables, I was hoping to use 'inter-app MIDI' and use another Android app to route the midi to the USB MIDI cable.
But I can't see how 'inter-app MIDI' works, and it's not in the manual either.

Any assistance much appreciated.
~W