1.1. Requirements Language (要求性用语)

本文中关键词 "MUST (必须)", "MUST NOT (绝对不得)", "REQUIRED (要求)", "SHALL (应当)", "SHALL NOT (不应)", "SHOULD (应该)", "SHOULD NOT (不应该)", "RECOMMENDED (推荐)", "MAY (可以)" 以及 "OPTIONAL (可选)" 仅在其为全大写时按 RFC 2119 [RFC2119] 所述解释. 它们也可能以小写或混合大小写形式出现, 作为普通英文词语, 不具有特殊含义.