2. Notational Conventions

关键词 "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY" 和 "OPTIONAL" 仅在全部大写出现时, 按 BCP 14 [RFC2119] [RFC8174] 解释.

ABNF definitions 使用 [RFC5234] 的 notation. 本文档未定义的 ABNF rules 在 [RFC5234] 中定义, 例如 CRLF, WSP, DQUOTE, VCHAR, ALPHA 和 DIGIT, 或在 [RFC6350] 中定义.