I'm trying to assign 4 pins from PORTA as the CHSEL f/register as follows;

CHSEL = PORTA.1.2.3.4
Get this error;
C:\PBP\PLL-CPU.BAS ERROR Line 24: Bad variable modifier: .1.2.3.4
I've tried different variations on this (1-4) (1234) etc. but with the same results.
What is the correct syntax for doing this? I only want to use these 4 pins.