Notionally, a fully loaded SV looks vaguely like this:

SV*->[ SVANY ]->[   IV   ]
     [ FLAGS ]  [   NV   ]
                [   PV   ]->"some text"
    
What my code above does is this:    

SV*->[ SVANY ]->[   IV   ]
     [ FLAGS ]  [   NV   ]<-+
                [   PV   ]--+    Point the PV at the memory holding the NV.