System Variables are not "variables"

A system variable is not defined and stored as a proper variable the same way all other vars are. For example, CHKVAR will always return false (0) for a system variable—even a writeable one. In addition, accessing a system variable through functional VAR will throw Undefined variable. Take the following prompt as an example (lines starting with > are DIRECT input, all others are output.)

>PRINT CHKVAR("MAINCNT")
 0
 OK
>PRINT VAR("CSRX")
 Undefined variable
 OK
>VAR A%=10
 OK
>PRINT CHKVAR("A%")
 1
 OK
>PRINT VAR("A%")
 10
 OK

This leads to the conclusion that system variables are specially compiled keywords and not variables which point to some static system value; even writeable ones probably compile to a special assignment instruction when writing. This also possibly confirms the suspicion that TRUE and FALSE are complied keywords which simply represent 1 and 0, instead of being true variables themselves, making their associated constants redundant.