Compound expression and order of evaluation

Hi,

Can anybody confirm for that in the following code, that the regsub
expression is always evaulated first, so that I can be certain that
Extras will always be correctly set? I've looked on the Wiki and in
"Practical Programming" but I cannot find the answer.

Many thanks,

Jo.

set Extras "xx"
set LengthCheck 12
set BitMap "101010101010"

if {([regsub -all {[0-1]} $BitMap "" Extras] == $LengthCheck) &&
([string length $Extras] == 0)} {
.
.
.

.