Standards Speak

If you read many standards documents, apart from the need for excessive amounts of coffee, you'll also need to be wary of the overloaded meaning of some words.

Standards use shall to indicate something that is absolutely mandatory (or for 'shall not' absolutely forbidden). Violate a 'shall' and you are not conforming to the standard. The words required or must are synonyms.

The word should is weaker. 'Should' indicates a recommendation. The standard would like to you to follow it, but you're not breaking the standard if you don't. Recommended is a synonym.

May indicates an optional feature. You should be able to work with an implementation gracefully if it's present or if it's missing.

You can find a more official version of the above as RFC 2119.

Things that are normative are part of the standard. Sections that are non-normative are things like background information and clarifications. Sometimes suggested implementation techniques are suggested in a non-normative section because they help clarify the concepts in the standard, but the writers rightly don't want to constrain implementers.