1.3 How to Read This Book
1.3.1 Normative keywords #
The key words MUST, MUST NOT, SHOULD, SHOULD NOT, and MAY in this document are to be interpreted as described in RFC 2119. Their meaning within a specification is defined in §2.1.
Text set off as a note is informative.
1.3.2 The two halves carry different weight, deliberately #
Chapters 2 and 3 govern specifications and are normative throughout. A specification that violates one of their requirements is malformed, and the requirement is stated as such.
Chapter 4 governs technical reference manuals and is deliberately lighter. Most of it is SHOULD and MAY, and some of it is offered as guidance carrying no normative weight at all. A manual is a description of software rather than a contract, so prescribing its shape tightly would be prescribing the shape of the software.
Two rules in chapter 4 are exceptions and are stated as MUST NOT, because they are what makes the class a class rather than a matter of taste: a manual carries no RFC 2119 keywords (§4.2), and a manual does not narrate the difference between itself and a specification (§4.4).
Chapters 5 and 6 apply to both classes.
1.3.3 Reading order #
An implementer needs §2.1 and chapter 5, and nothing else.
An author needs the chapter for the class they are writing, then chapters 5 and 6.
A reader trying to work out which class a document belongs to, or why a given fact is documented in one place rather than another, wants §1.2.