[1]

A single Unicode code point is denoted by "U+" followed by four to six hexadecimal digits, while a range of Unicode code points is denoted by two hexadecimal numbers separated by "..", with no prefixes.

[2] RFC 3490 - Internationalizing Domain Names in Applications (IDNA) http://tools.ietf.org/html/rfc3490#section-2、 [3] RFC 3492 - Punycode: A Bootstring encoding of Unicode for Internationalized Domain Names in Applications (IDNA) http://tools.ietf.org/html/rfc3492#section-2
[14] U+ の応用

[4] RFC 5890 - Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework ( ( 版)) http://tools.ietf.org/html/rfc5890#section-2.1

[5] Unicode Mail List Archive: Re: Origin of the U+nnnn notation ( (Kenneth Whistler (kenw@sybase.com) 著, 版)) http://unicode.org/mail-arch/unicode-ml/y2005-m11/0060.html

[6] Selector parsing: It's easy to hit unexpected unicode-range tokens ( (Boris Zbarsky 著, 版)) http://lists.w3.org/Archives/Public/www-style/2014Jun/0486.html

[7] [css-syntax][css-fonts] Wrapping up the <unicode-range> thing (Tab Atkins Jr. 著, 版) https://lists.w3.org/Archives/Public/www-style/2015Jun/0286.html

[8] 多符号化対応w3mの追加設定項目 () http://pub.ks-and-ks.ne.jp/prog/w3mmee/config.shtml.ja#non-ucs

[9] RDF 1.1 N-Triples (, ) https://www.w3.org/TR/n-triples/#h2_n-triples-grammar

Unicode code points only in the range U+0 to U+10FFFF inclusive are allowed.