expand: add explanation to 'conservative'

The variable 'conservative' is used to allow testing some
characteristics of an expression while inhibiting any possible
side-efects like issuing a warning or marking the expression
as erroneous. But this role is not immedialtely apparent.

So, add a comment to the variable declaration.

Suggested-by: Thomas WeiƟschuh <thomas@t-8ch.de>
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
1 file changed