Pedantic about rules
Behaviour
Your client is pedantic about rules no matter how important.
A person may come to you with what they see as even tiny infraction to a rule. They may know the "rule book" better than you and will see even a small change to a rule as a big deal.
To many people such behaviour will seem too pedantic, inflexible or even intentionally disruptive. You may even feel that such a person is trying to game the system. But that's not the case at all.
People on the autism spectrum will often rely on learning the rules to get by. They have to use rules to deal with situations where others just "instinctively" know what to do. That's why they feel that all rules are equally important.
Difficulty
Your client may have problems with reading notes, sequencing, understanding time or following instructions.
People on the autism spectrum rely on rules to navigate situations that others handle intuitively. All rules feel equally important to them.