I was a little puzzled by that too.  The reference to Adjusted Gross Income seemed sufficient to me, I have no idea why they cherry-picked certain adjustments.  I'd have to dig a little deeper into other existing definitions of AGI in the code to try to shed some light on it.

So even if this passes as-is there are already a plethora of "what about" questions that will need to be clarified by the IRS before anyone can program changes into tax software.  Fun.