All parts of this specification are normative, with the EXCEPTION of notes, examples, and sections explicitly marked as Non-Normative.

The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this specification are to be interpreted as described in .

Each pattern is defined using a single expression constraining one or more items.

Each pattern is identified using a unique and stable URI .

Assertions about documents and implementations that are not enforced by the normative patterns are marked by a dagger symbol (†) at the end of a sentence. Each assertion has been assigned a unique and stable identifier. The assertion identifiers may be used by implementations of this specification for any purpose, such as error reporting. The assertions and their identifiers are summarized in section .