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2. Notational Conventions

This section defines the notation and terminology used throughout this specification.

RFC 2119 Keywords​

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, RFC 2119, as scoped to those conformance targets.

ABNF Notation​

This document uses the Augmented Backus-Naur Form (ABNF) notation of RFC 2616, and explicitly includes the following rules from it:

  • quoted-string
  • token
  • SP (space)
  • LOALPHA
  • DIGIT

Additional Rules​

The following rules are included from various specifications:

From RFC 3986:

  • URI
  • URI-Reference

From RFC 4288:

  • type-name
  • subtype-name

From W3C HTML 4.01:

  • MediaDesc

From RFC 5646:

  • Language-Tag

From RFC 5987:

  • ext-value
  • parmname

Note: These notational conventions ensure precise specification of syntax elements used in the Link header field and related structures.

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