CHSEL VAR PORTA

This will assign the whole PORTA, all the time to chsel variable... it's a simple alias. Still, it's the WHOLE PORTA reading, you still need to remove the bit you don't want/need.

If you want to assign a single pin to a variable
A_SINGLE_PIN VAR PORTA.0

As far as I'm aware of, there's no shortcuts. Bitwise & Logical mask/operations are indeed listed in the manual, not explained as it's a basic knowledge you should already be aware of when programming. Case not, there's Wikipedia & Google
http://en.wikipedia.org/wiki/Bitwise_operation
http://www.ralphb.net/IPSubnet/logical.html
and so forth