I think the issue is different. It’s not whether “shall” means something other than “must”; rather the issue concerns the scope of the code section containing this language. For example, in the California Rules of Court, you can find a rule that that briefs “must” use 13-point type. (Rule 8.204(b)(4).) That provision is located within the title on appellate procedure, so it has no effect on trial briefs. Even if it said “absolutely shall with no exceptions whatsoever and under penalty of death,” it would have no effect in a trial proceeding.