What is GPUREG_ATTRIBBUFFERi_CONFIG0?

I've been looking at the portal3ds source code, and can't figure out what the GPUREG_ATTRIBBUFFERi_CONFIG0 register is for, as I can't find it in the internal registers page of 3dbrew. That being said, I suspect it to be an early define for GPUREG_ATTRIBBUFFERi_OFFSET.
But then, what's the difference between it
and GPUREG_VERTEX_OFFSET?

Any help is appreciated!!