JSON Unicode转义序列-是否小写？

Question

我正在阅读RFC 4627，但无法确定以下内容是否为有效JSON。考虑以下简约的JSON文本:

["\u005c"]

问题是小写的 c。

根据RFC的文本，允许:

Any character may be escaped. If the character is in the Basic Multilingual Plane (U+0000 through U+FFFF), then it may be represented as a six-character sequence: a reverse solidus, followed by the lowercase letter u, followed by four hexadecimal digits that encode the character's code point. The hexadecimal letters A though F can be upper or lowercase. So, for example, a string containing only a single reverse solidus character may be represented as "\u005C".

(强调我的)

问题在于RFC还包含以下语法:

char = unescaped /
       escape (
           %x22 /          ; "    quotation mark  U+0022
           %x5C /          ; \    reverse solidus U+005C
           %x2F /          ; /    solidus         U+002F
           %x62 /          ; b    backspace       U+0008
           %x66 /          ; f    form feed       U+000C
           %x6E /          ; n    line feed       U+000A
           %x72 /          ; r    carriage return U+000D
           %x74 /          ; t    tab             U+0009
           %x75 4HEXDIG )  ; uXXXX                U+XXXX

其中HEXDIG在引用RFC 4234中定义为

HEXDIG         =  DIGIT / "A" / "B" / "C" / "D" / "E" / "F"

其中仅包含大写字母。

FWIW，根据我的研究，大多数JSON解析器都接受大写和小写字母。

问题:实际正确的是什么？是否存在矛盾，并且RFC中的语法应该固定？

Answer 1

我认为这是RFC 4234的这一部分所解释的:

ABNF strings are case-insensitive and the character set for these strings is us-ascii.

Hence:

    rulename = "abc"

and:

    rulename = "aBc"

will match "abc", "Abc", "aBc", "abC", "ABc", "aBC", "AbC", and "ABC".

另一方面，后续部分并不十分清楚:

To specify a rule that IS case SENSITIVE, specify the characters individually.

For example:

    rulename    =  %d97 %d98 %d99

or

    rulename    =  %d97.98.99

在HEXDIG规则的情况下，它们是以-开头的单个字符，但是从字面上将它们指定为"A"等，而不是%d41，因此我怀疑这意味着它们不区分大小写。这不是我读过的最清晰的规范:(