由 HTTP 增强的 ABNF：#symbol 的规范参考
ABNF augmented by HTTP : normative reference for #symbol
上下文
解决 CORS 问题，我想知道 HTTP 响应的有效值是什么 header Access-Control-Allow-Headers.
Whatwg CORS spec on header syntax 在 ABNF 中告诉我：
Access-Control-Allow-Headers = #field-name
RFC7230 告诉我：
field-name = token
token = 1*tchar
tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
另外，Whatwg states那：
ABNF means ABNF as augmented by HTTP (in particular the addition #) and RFC 7405. [RFC7405]
好的，我现在知道这个回复header是无效的：
Access-Control-Allow-Headers: Origin, Content-Type, content type, Accept, Authorization
field-name 不应包含白色 space，但这引出了我的问题：
问题
whatwg ABNF中#symbol的规范参考在哪里？它不是定义 ABNF 语法的 RFC5234 。我猜这是一个逗号分隔的字段，但我没有找到真正的参考。
PS：问题不是“Access-Control-Allow-Headers 的有效值是什么”
这个 “由 HTTP 增强（特别是添加 #）” 来自 RFC 7230 - Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing section 7. ABNF List Extension: #rule:
A #rule extension to the ABNF rules of [RFC5234] is used to improve
readability in the definitions of some header field values.
A construct "#" is defined, similar to "*", for defining
comma-delimited lists of elements. The full form is "<n>#<m>element"
indicating at least <n> and at most <m> elements, each separated by a
single comma (",") and optional whitespace (OWS).
In any production that uses the list construct, a sender must not
generate empty list elements. In other words, a sender must generate
lists that satisfy the following syntax:
1#element => element *( OWS "," OWS element )
(...)
因此 #field-name 变为“零个或多个 field-name（以逗号分隔并由可选的线性空格包围）”，因为 n 和 m 分别默认为 0 和无穷大。
上下文
解决 CORS 问题，我想知道 HTTP 响应的有效值是什么 header Access-Control-Allow-Headers.
Whatwg CORS spec on header syntax 在 ABNF 中告诉我：
Access-Control-Allow-Headers = #field-name
RFC7230 告诉我：
field-name = token
token = 1*tchar
tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
另外，Whatwg states那：
ABNF means ABNF as augmented by HTTP (in particular the addition #) and RFC 7405. [RFC7405]
好的，我现在知道这个回复header是无效的：
Access-Control-Allow-Headers: Origin, Content-Type, content type, Accept, Authorization
field-name 不应包含白色 space，但这引出了我的问题：
问题
whatwg ABNF中#symbol的规范参考在哪里？它不是定义 ABNF 语法的 RFC5234 。我猜这是一个逗号分隔的字段，但我没有找到真正的参考。
PS：问题不是“Access-Control-Allow-Headers 的有效值是什么”
这个 “由 HTTP 增强（特别是添加 #）” 来自 RFC 7230 - Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing section 7. ABNF List Extension: #rule:
A #rule extension to the ABNF rules of [RFC5234] is used to improve readability in the definitions of some header field values.
A construct "#" is defined, similar to "*", for defining comma-delimited lists of elements. The full form is "
<n>#<m>element" indicating at least<n>and at most<m>elements, each separated by a single comma (",") and optional whitespace (OWS).In any production that uses the list construct, a sender must not generate empty list elements. In other words, a sender must generate lists that satisfy the following syntax:
1#element => element *( OWS "," OWS element )
(...)
因此 #field-name 变为“零个或多个 field-name（以逗号分隔并由可选的线性空格包围）”，因为 n 和 m 分别默认为 0 和无穷大。