以下核心规则包含在RFC RFC347的附录B.1中:ALPHA(字母),CR(回车),CRLF(CR LF),CTL(对照),DIGIT(十进制0-9) ,DQUOTE(双引号),HEXDIG(十六进制0-9 / AF / a-f),LF(换行),OCTET(任何8位数据序列),SP(空格)和VCHAR(任何可见的US-ASCII字符)。
下列规则定义在RFC7230:
BWS = <BWS, see [RFC7230], Section 3.2.3>
OWS = <OWS, see [RFC7230], Section 3.2.3>
quoted-string = <quoted-string, see [RFC7230], Section 3.2.6>
token = <token, see [RFC7230], Section 3.2.6>