Characters and digits of Chapter four of the Unicode Standard

Question

In a language specification, there is

name-start-character=
'_' | '\' | ? any code points which are characters as defined by the Unicode character properties, chapter four of the Unicode Standard ?;

Could anyone tell me how to correctly represent that any code points which are characters as defined by the Unicode character properties, chapter four of the Unicode Standard in a lexer?

Similarly, there is

name-character=
name-start-character | decimal-digit | full-stop | ? any code points which are digits
as defined by the Unicode character properties, chapter four of the Unicode standard ?;

Does anyone know how to faithfully represent that any code points which are digits as defined by the Unicode character properties, chapter four of the Unicode standard in a lexer?

I have found this, but it is too hard for me to understand.

PS: I use sedlex to write my lexer.

Edit 1:

Previously, I used the following code to make name_start_character. Even though it was not fully complete, it worked more or less.

let first_Latin_identifier_character = [%sedlex.regexp? ('a'..'z') | ('A'..'Z') ]
let subsequent_Latin_identifier_character = [%sedlex.regexp? first_Latin_identifier_character | '\x5F' (* underscore *) | ('0'..'9')]
let latin_identifier = [%sedlex.regexp? first_Latin_identifier_character, (Star subsequent_Latin_identifier_character)]

let cP936_initial_character = [%sedlex.regexp? 0xff21 .. 0xff3a | 0xff41 .. 0xff5a | 0x3001 .. 0x2014 | 0x2016 .. 0x2026 | 0x3014 .. 0x2103 | 0x00a4 .. 0x2605 | 0x2488 .. 0x216b | 0x3041 .. 0xfa29]
let cP936_subsequent_character = [%sedlex.regexp? cP936_initial_character | 0xff3f | 0xff10 .. 0xff19]
let first_sChinese_identifier_character = [%sedlex.regexp? first_Latin_identifier_character | cP936_initial_character]
let subsequent_sChinese_identifier_character = [%sedlex.regexp? subsequent_Latin_identifier_character | cP936_subsequent_character]
let simplified_Chinese_identifier = [%sedlex.regexp? first_sChinese_identifier_character, (Star subsequent_sChinese_identifier_character)]

let cjk_character = [%sedlex.regexp? 0x4E00 .. 0x9FFF | 0x3400 .. 0x4DBF | 0x20000 .. 0x2A6DF | 0x2A700 .. 0x2B73F | 0x2B740 .. 0x2B81F |
                            0x2B820 .. 0x2CEAF | 0xF900 .. 0xFAFF | 0x2F800 .. 0x2FA1F]
let cjk_identifier = [%sedlex.regexp? (Plus cjk_character)]


let korean_character = [%sedlex.regexp? 0xAC00 .. 0xD7A3]
let korean_identifier = [%sedlex.regexp? Plus korean_character]

let japanese_character = [%sedlex.regexp? 0x3000 .. 0x303f | 0x3040 .. 0x309f | 0x30a0 .. 0x30ff | 0xff00 .. 0xffef] (* except CJK unifed ideographs - Common and uncommon kanji (4e00 - 9faf) *)
let japanese_identifier = [%sedlex.regexp? Plus japanese_character]

let cP2_character_874 = [%sedlex.regexp? 0x20ac|0x0081|0x0082|0x0083|0x0084|0x2026|0x0086|0x0087|0x0088|0x0089|0x008a|0x008b|0x008c|0x008d|0x008e|0x008f|0x0090|0x2018|0x2019|0x201c|0x201d|0x2022|0x2013|0x2014|0x0098|0x0099|0x009a|0x009b|0x009c|0x009d|0x009e|0x009f|0x00a0|0x0e01|0x0e02|0x0e03|0x0e04|0x0e05|0x0e06|0x0e07|0x0e08|0x0e09|0x0e0a|0x0e0b|0x0e0c|0x0e0d|0x0e0e|0x0e0f|0x0e10|0x0e11|0x0e12|0x0e13|0x0e14|0x0e15|0x0e16|0x0e17|0x0e18|0x0e19|0x0e1a|0x0e1b|0x0e1c|0x0e1d|0x0e1e|0x0e1f|0x0e20|0x0e21|0x0e22|0x0e23|0x0e24|0x0e25|0x0e26|0x0e27|0x0e28|0x0e29|0x0e2a|0x0e2b|0x0e2c|0x0e2d|0x0e2e|0x0e2f|0x0e30|0x0e31|0x0e32|0x0e33|0x0e34|0x0e35|0x0e36|0x0e37|0x0e38|0x0e39|0x0e3a|0xf8c1|0xf8c2|0xf8c3|0xf8c4|0x0e3f|0x0e40|0x0e41|0x0e42|0x0e43|0x0e44|0x0e45|0x0e46|0x0e47|0x0e48|0x0e49|0x0e4a|0x0e4b|0x0e4c|0x0e4d|0x0e4e|0x0e4f|0x0e50|0x0e51|0x0e52|0x0e53|0x0e54|0x0e55|0x0e56|0x0e57|0x0e58|0x0e59|0x0e5a|0x0e5b|0xf8c5|0xf8c6|0xf8c7|0xf8c8]
let cP2_character_1250 = [%sedlex.regexp? 0x20ac|0x0081|0x201a|0x0083|0x201e|0x2026|0x2020|0x2021|0x0088|0x2030|0x0160|0x2039|0x015a|0x0164|0x017d|0x0179|0x0090|0x2018|0x2019|0x201c|0x201d|0x2022|0x2013|0x2014|0x0098|0x2122|0x0161|0x203a|0x015b|0x0165|0x017e|0x017a|0x00a0|0x02c7|0x02d8|0x0141|0x00a4|0x0104|0x00a6|0x00a7|0x00a8|0x00a9|0x015e|0x00ab|0x00ac|0x00ad|0x00ae|0x017b|0x00b0|0x00b1|0x02db|0x0142|0x00b4|0x00b5|0x00b6|0x00b7|0x00b8|0x0105|0x015f|0x00bb|0x013d|0x02dd|0x013e|0x017c|0x0154|0x00c1|0x00c2|0x0102|0x00c4|0x0139|0x0106|0x00c7|0x010c|0x00c9|0x0118|0x00cb|0x011a|0x00cd|0x00ce|0x010e|0x0110|0x0143|0x0147|0x00d3|0x00d4|0x0150|0x00d6|0x00d7|0x0158|0x016e|0x00da|0x0170|0x00dc|0x00dd|0x0162|0x00df|0x0155|0x00e1|0x00e2|0x0103|0x00e4|0x013a|0x0107|0x00e7|0x010d|0x00e9|0x0119|0x00eb|0x011b|0x00ed|0x00ee|0x010f|0x0111|0x0144|0x0148|0x00f3|0x00f4|0x0151|0x00f6|0x00f7|0x0159|0x016f|0x00fa|0x0171|0x00fc|0x00fd|0x0163|0x02d9]
let cP2_character_1251 = [%sedlex.regexp? 0x0402|0x0403|0x201a|0x0453|0x201e|0x2026|0x2020|0x2021|0x20ac|0x2030|0x0409|0x2039|0x040a|0x040c|0x040b|0x040f|0x0452|0x2018|0x2019|0x201c|0x201d|0x2022|0x2013|0x2014|0x0098|0x2122|0x0459|0x203a|0x045a|0x045c|0x045b|0x045f|0x00a0|0x040e|0x045e|0x0408|0x00a4|0x0490|0x00a6|0x00a7|0x0401|0x00a9|0x0404|0x00ab|0x00ac|0x00ad|0x00ae|0x0407|0x00b0|0x00b1|0x0406|0x0456|0x0491|0x00b5|0x00b6|0x00b7|0x0451|0x2116|0x0454|0x00bb|0x0458|0x0405|0x0455|0x0457|0x0410|0x0411|0x0412|0x0413|0x0414|0x0415|0x0416|0x0417|0x0418|0x0419|0x041a|0x041b|0x041c|0x041d|0x041e|0x041f|0x0420|0x0421|0x0422|0x0423|0x0424|0x0425|0x0426|0x0427|0x0428|0x0429|0x042a|0x042b|0x042c|0x042d|0x042e|0x042f|0x0430|0x0431|0x0432|0x0433|0x0434|0x0435|0x0436|0x0437|0x0438|0x0439|0x043a|0x043b|0x043c|0x043d|0x043e|0x043f|0x0440|0x0441|0x0442|0x0443|0x0444|0x0445|0x0446|0x0447|0x0448|0x0449|0x044a|0x044b|0x044c|0x044d|0x044e|0x044f]
let cP2_character_1252 = [%sedlex.regexp? 0x20ac|0x0081|0x201a|0x0192|0x201e|0x2026|0x2020|0x2021|0x02c6|0x2030|0x0160|0x2039|0x0152|0x008d|0x017d|0x008f|0x0090|0x2018|0x2019|0x201c|0x201d|0x2022|0x2013|0x2014|0x02dc|0x2122|0x0161|0x203a|0x0153|0x009d|0x017e|0x0178|0x00a0|0x00a1|0x00a2|0x00a3|0x00a4|0x00a5|0x00a6|0x00a7|0x00a8|0x00a9|0x00aa|0x00ab|0x00ac|0x00ad|0x00ae|0x00af|0x00b0|0x00b1|0x00b2|0x00b3|0x00b4|0x00b5|0x00b6|0x00b7|0x00b8|0x00b9|0x00ba|0x00bb|0x00bc|0x00bd|0x00be|0x00bf|0x00c0|0x00c1|0x00c2|0x00c3|0x00c4|0x00c5|0x00c6|0x00c7|0x00c8|0x00c9|0x00ca|0x00cb|0x00cc|0x00cd|0x00ce|0x00cf|0x00d0|0x00d1|0x00d2|0x00d3|0x00d4|0x00d5|0x00d6|0x00d7|0x00d8|0x00d9|0x00da|0x00db|0x00dc|0x00dd|0x00de|0x00df|0x00e0|0x00e1|0x00e2|0x00e3|0x00e4|0x00e5|0x00e6|0x00e7|0x00e8|0x00e9|0x00ea|0x00eb|0x00ec|0x00ed|0x00ee|0x00ef|0x00f0|0x00f1|0x00f2|0x00f3|0x00f4|0x00f5|0x00f6|0x00f7|0x00f8|0x00f9|0x00fa|0x00fb|0x00fc|0x00fd|0x00fe|0x00ff]
let cP2_character_1253 = [%sedlex.regexp? 0x20ac|0x0081|0x201a|0x0192|0x201e|0x2026|0x2020|0x2021|0x0088|0x2030|0x008a|0x2039|0x008c|0x008d|0x008e|0x008f|0x0090|0x2018|0x2019|0x201c|0x201d|0x2022|0x2013|0x2014|0x0098|0x2122|0x009a|0x203a|0x009c|0x009d|0x009e|0x009f|0x00a0|0x0385|0x0386|0x00a3|0x00a4|0x00a5|0x00a6|0x00a7|0x00a8|0x00a9|0xf8f9|0x00ab|0x00ac|0x00ad|0x00ae|0x2015|0x00b0|0x00b1|0x00b2|0x00b3|0x0384|0x00b5|0x00b6|0x00b7|0x0388|0x0389|0x038a|0x00bb|0x038c|0x00bd|0x038e|0x038f|0x0390|0x0391|0x0392|0x0393|0x0394|0x0395|0x0396|0x0397|0x0398|0x0399|0x039a|0x039b|0x039c|0x039d|0x039e|0x039f|0x03a0|0x03a1|0xf8fa|0x03a3|0x03a4|0x03a5|0x03a6|0x03a7|0x03a8|0x03a9|0x03aa|0x03ab|0x03ac|0x03ad|0x03ae|0x03af|0x03b0|0x03b1|0x03b2|0x03b3|0x03b4|0x03b5|0x03b6|0x03b7|0x03b8|0x03b9|0x03ba|0x03bb|0x03bc|0x03bd|0x03be|0x03bf|0x03c0|0x03c1|0x03c2|0x03c3|0x03c4|0x03c5|0x03c6|0x03c7|0x03c8|0x03c9|0x03ca|0x03cb|0x03cc|0x03cd|0x03ce|0xf8fb]
let cP2_character_1254 = [%sedlex.regexp? 0x20ac|0x0081|0x201a|0x0192|0x201e|0x2026|0x2020|0x2021|0x02c6|0x2030|0x0160|0x2039|0x0152|0x008d|0x008e|0x008f|0x0090|0x2018|0x2019|0x201c|0x201d|0x2022|0x2013|0x2014|0x02dc|0x2122|0x0161|0x203a|0x0153|0x009d|0x009e|0x0178|0x00a0|0x00a1|0x00a2|0x00a3|0x00a4|0x00a5|0x00a6|0x00a7|0x00a8|0x00a9|0x00aa|0x00ab|0x00ac|0x00ad|0x00ae|0x00af|0x00b0|0x00b1|0x00b2|0x00b3|0x00b4|0x00b5|0x00b6|0x00b7|0x00b8|0x00b9|0x00ba|0x00bb|0x00bc|0x00bd|0x00be|0x00bf|0x00c0|0x00c1|0x00c2|0x00c3|0x00c4|0x00c5|0x00c6|0x00c7|0x00c8|0x00c9|0x00ca|0x00cb|0x00cc|0x00cd|0x00ce|0x00cf|0x011e|0x00d1|0x00d2|0x00d3|0x00d4|0x00d5|0x00d6|0x00d7|0x00d8|0x00d9|0x00da|0x00db|0x00dc|0x0130|0x015e|0x00df|0x00e0|0x00e1|0x00e2|0x00e3|0x00e4|0x00e5|0x00e6|0x00e7|0x00e8|0x00e9|0x00ea|0x00eb|0x00ec|0x00ed|0x00ee|0x00ef|0x011f|0x00f1|0x00f2|0x00f3|0x00f4|0x00f5|0x00f6|0x00f7|0x00f8|0x00f9|0x00fa|0x00fb|0x00fc|0x0131|0x015f|0x00ff]
let cP2_character_1255 = [%sedlex.regexp? 0x20ac|0x0081|0x201a|0x0192|0x201e|0x2026|0x2020|0x2021|0x02c6|0x2030|0x008a|0x2039|0x008c|0x008d|0x008e|0x008f|0x0090|0x2018|0x2019|0x201c|0x201d|0x2022|0x2013|0x2014|0x02dc|0x2122|0x009a|0x203a|0x009c|0x009d|0x009e|0x009f|0x00a0|0x00a1|0x00a2|0x00a3|0x20aa|0x00a5|0x00a6|0x00a7|0x00a8|0x00a9|0x00d7|0x00ab|0x00ac|0x00ad|0x00ae|0x00af|0x00b0|0x00b1|0x00b2|0x00b3|0x00b4|0x00b5|0x00b6|0x00b7|0x00b8|0x00b9|0x00f7|0x00bb|0x00bc|0x00bd|0x00be|0x00bf|0x05b0|0x05b1|0x05b2|0x05b3|0x05b4|0x05b5|0x05b6|0x05b7|0x05b8|0x05b9|0x05ba|0x05bb|0x05bc|0x05bd|0x05be|0x05bf|0x05c0|0x05c1|0x05c2|0x05c3|0x05f0|0x05f1|0x05f2|0x05f3|0x05f4|0xf88d|0xf88e|0xf88f|0xf890|0xf891|0xf892|0xf893|0x05d0|0x05d1|0x05d2|0x05d3|0x05d4|0x05d5|0x05d6|0x05d7|0x05d8|0x05d9|0x05da|0x05db|0x05dc|0x05dd|0x05de|0x05df|0x05e0|0x05e1|0x05e2|0x05e3|0x05e4|0x05e5|0x05e6|0x05e7|0x05e8|0x05e9|0x05ea|0xf894|0xf895|0x200e|0x200f|0xf896]
let cP2_character_1256 = [%sedlex.regexp? 0x20ac|0x067e|0x201a|0x0192|0x201e|0x2026|0x2020|0x2021|0x02c6|0x2030|0x0679|0x2039|0x0152|0x0686|0x0698|0x0688|0x06af|0x2018|0x2019|0x201c|0x201d|0x2022|0x2013|0x2014|0x06a9|0x2122|0x0691|0x203a|0x0153|0x200c|0x200d|0x06ba|0x00a0|0x060c|0x00a2|0x00a3|0x00a4|0x00a5|0x00a6|0x00a7|0x00a8|0x00a9|0x06be|0x00ab|0x00ac|0x00ad|0x00ae|0x00af|0x00b0|0x00b1|0x00b2|0x00b3|0x00b4|0x00b5|0x00b6|0x00b7|0x00b8|0x00b9|0x061b|0x00bb|0x00bc|0x00bd|0x00be|0x061f|0x06c1|0x0621|0x0622|0x0623|0x0624|0x0625|0x0626|0x0627|0x0628|0x0629|0x062a|0x062b|0x062c|0x062d|0x062e|0x062f|0x0630|0x0631|0x0632|0x0633|0x0634|0x0635|0x0636|0x00d7|0x0637|0x0638|0x0639|0x063a|0x0640|0x0641|0x0642|0x0643|0x00e0|0x0644|0x00e2|0x0645|0x0646|0x0647|0x0648|0x00e7|0x00e8|0x00e9|0x00ea|0x00eb|0x0649|0x064a|0x00ee|0x00ef|0x064b|0x064c|0x064d|0x064e|0x00f4|0x064f|0x0650|0x00f7|0x0651|0x00f9|0x0652|0x00fb|0x00fc|0x200e|0x200f|0x06d2]
let cP2_character_1257 = [%sedlex.regexp? 0x20ac|0x0081|0x201a|0x0083|0x201e|0x2026|0x2020|0x2021|0x0088|0x2030|0x008a|0x2039|0x008c|0x00a8|0x02c7|0x00b8|0x0090|0x2018|0x2019|0x201c|0x201d|0x2022|0x2013|0x2014|0x0098|0x2122|0x009a|0x203a|0x009c|0x00af|0x02db|0x009f|0x00a0|0xf8fc|0x00a2|0x00a3|0x00a4|0xf8fd|0x00a6|0x00a7|0x00d8|0x00a9|0x0156|0x00ab|0x00ac|0x00ad|0x00ae|0x00c6|0x00b0|0x00b1|0x00b2|0x00b3|0x00b4|0x00b5|0x00b6|0x00b7|0x00f8|0x00b9|0x0157|0x00bb|0x00bc|0x00bd|0x00be|0x00e6|0x0104|0x012e|0x0100|0x0106|0x00c4|0x00c5|0x0118|0x0112|0x010c|0x00c9|0x0179|0x0116|0x0122|0x0136|0x012a|0x013b|0x0160|0x0143|0x0145|0x00d3|0x014c|0x00d5|0x00d6|0x00d7|0x0172|0x0141|0x015a|0x016a|0x00dc|0x017b|0x017d|0x00df|0x0105|0x012f|0x0101|0x0107|0x00e4|0x00e5|0x0119|0x0113|0x010d|0x00e9|0x017a|0x0117|0x0123|0x0137|0x012b|0x013c|0x0161|0x0144|0x0146|0x00f3|0x014d|0x00f5|0x00f6|0x00f7|0x0173|0x0142|0x015b|0x016b|0x00fc|0x017c|0x017e|0x02d9]
let cP2_character_1258 = [%sedlex.regexp? 0x20ac|0x0081|0x201a|0x0192|0x201e|0x2026|0x2020|0x2021|0x02c6|0x2030|0x008a|0x2039|0x0152|0x008d|0x008e|0x008f|0x0090|0x2018|0x2019|0x201c|0x201d|0x2022|0x2013|0x2014|0x02dc|0x2122|0x009a|0x203a|0x0153|0x009d|0x009e|0x0178|0x00a0|0x00a1|0x00a2|0x00a3|0x00a4|0x00a5|0x00a6|0x00a7|0x00a8|0x00a9|0x00aa|0x00ab|0x00ac|0x00ad|0x00ae|0x00af|0x00b0|0x00b1|0x00b2|0x00b3|0x00b4|0x00b5|0x00b6|0x00b7|0x00b8|0x00b9|0x00ba|0x00bb|0x00bc|0x00bd|0x00be|0x00bf|0x00c0|0x00c1|0x00c2|0x0102|0x00c4|0x00c5|0x00c6|0x00c7|0x00c8|0x00c9|0x00ca|0x00cb|0x0300|0x00cd|0x00ce|0x00cf|0x0110|0x00d1|0x0309|0x00d3|0x00d4|0x01a0|0x00d6|0x00d7|0x00d8|0x00d9|0x00da|0x00db|0x00dc|0x01af|0x0303|0x00df|0x00e0|0x00e1|0x00e2|0x0103|0x00e4|0x00e5|0x00e6|0x00e7|0x00e8|0x00e9|0x00ea|0x00eb|0x0301|0x00ed|0x00ee|0x00ef|0x0111|0x00f1|0x0323|0x00f3|0x00f4|0x01a1|0x00f6|0x00f7|0x00f8|0x00f9|0x00fa|0x00fb|0x00fc|0x01b0|0x20ab|0x00ff]

let cP2_character = [%sedlex.regexp? cP2_character_874 | cP2_character_1250 | cP2_character_1251 | cP2_character_1252
                                      | cP2_character_1253 | cP2_character_1254 | cP2_character_1255 | cP2_character_1256 
                                      | cP2_character_1257 | cP2_character_1258]

let codepage_identifier = [%sedlex.regexp? (first_Latin_identifier_character | cP2_character), Star (subsequent_Latin_identifier_character | cP2_character)]

let name_start_character = [%sedlex.regexp? '_' | '\x5C' | 
  first_Latin_identifier_character | 
  cP2_character |
  cjk_character | 
  korean_character | 
  japanese_character]

Then, I tried rici's simpler solution:

let name_start_character = [%sedlex.regexp? '_' | '\x5C' | Compl (cn | cs)]

It returned Fatal error: exception Stack overflow followed by Error: Error while running external preprocessor

Answer 1

In brief, Chapter 4 defines a number of properties which indicate information about characters. This can indicate e.g. "this is a whitespace character", "this is a combining character", etc, and, predictably, "this is a digit". Also, paradoxically, "this is not a character".

How to reliably and robustly codify this information in a lexer depends on that particular lexer's requirements, and also on whether you need to update it when Unicode is updated, or if a static snapshot of the current Unicode standard is enough.

Either way, you will want to download and parse the Unicode Character Database and extract an enumeration of the code points with the properties you are asking about.

For a quick sampler of digits, e.g. https://www.fileformat.info/search/google.htm?q=nine brings up mostly characters which have the "decimal digit" property. When you visit the individual results, examine the "Category" field near the top of each individual page, and the Character.isDigit() field further down. https://www.fileformat.info/info/unicode/category/Nd/list.htm has a full listing of the members of the category. The parent page https://www.fileformat.info/info/unicode/category/index.htm has a list of all the categories, with links to similar individual category pages with lists of their members.

https://www.unicode.org/faq/private_use.html contains a section which explains and enumerates the stable set of 66 code points which are defined as "noncharacters". Any others would satisfy the first defintion in your question.

Answer 2

Sedlex, according to its documentation, has predefined regular expression classes, many of which correspond to the Unicode standard. I believe you can use these to easily satisfy the requirement, assuming that sedlex is built with the same or newer Unicode version as that used by the document you are parsing:

• Code points which are characters: Compl (cn | cs)
• Digits: nd

Code points which are characters

The set of "code points which are characters as defined by the Unicode character properties" is actually defined in chapter two of the Unicode standard, not chapter four. In the current version (14.0.0), the definition is shown in Table 2.3 on page 30 (which is page 23 of the linked PDF).

In Unicode, every codepoint has a two-letter "general-category", which is normative although not always very informative. Table 2.3 relates general categories to three possible "character status" values: "Assigned to abstract character", "Cannot be assigned to abstract character" and "Not assigned to abstract character", as follows:

• Cannot be assigned to abstract character: Cs
• Not assigned to abstract character: Cn
• Assigned to abstract character: Everything else.

It's worth noting that the 66 "non-characters" in the standard have category Cn, not Cs as one might expect. Nonetheless, the standard guarantees that these 66 characters will never be assigned. Category Cs refers to codepoints which can only be used in two-codepoint sequences ("surrogate pairs"), and only in UTF-16 encoding. A well-formed UTF-8 or UTF-32 sequence cannot contain surrogate codepoints. But it can contain "non-characters", even though the code doesn't actually map to a character. (Thus, "non-character" codes can be used internally as sentinels or for other purposes; surrogate codes cannot be used for any purpose other than their use in UTF-16 encoding.)

In short, you can get the set of codepoints mapped to characters in whatever Unicode version was used by sedlex to create its predefined patterns. That would be the categories cc, cf, co, ll, lm, lo, lt, lu, mc, me, mn, nd, nl, no, pc, pd, pe, pf, pi, po, ps, sc, sk, sm, so, zl, zp, zs, which I believe you can write as Compl (cs | cn). Note that the list of categories is fixed by the stability guarantees of the Unicode standard, but many of the categories may be extended with new characters in future versions.

Digits

The general categories themselves are explained (to some extent) in section 4.5 of Chapter 4. There is no category called "digits"; the closest one would be category Nd, which is "Numbers, decimal digits". I'd recommend using that one (nd in sedlex).