Re: link that explain ICU_LOCALE locale concept about local variant code and keywords.

code from https://www.postgresql.org/message-id/flat/5e756dd6-0e91-d778-96fd-b1bcb06c161a%402ndquadrant.com

DROP DATABASE IF EXISTS dbicu;
CREATE DATABASE dbicu LOCALE_PROVIDER icu LOCALE 'en_US' ICU_LOCALE 'en-u-kf-upper' template 'template0';
\c dbicu
CREATE COLLATION upperfirst (provider = icu, locale = 'en-u-kf-upper');
CREATE TABLE icu(def text, en text COLLATE "en_US", upfirst text COLLATE upperfirst);
INSERT INTO icu VALUES ('a', 'a', 'a'), ('b','b','b'), ('A','A','A'), ('B','B','B');
SELECT def AS def FROM icu ORDER BY def;
SELECT def AS en FROM icu ORDER BY en;
SELECT def AS upfirst FROM icu ORDER BY upfirst;
SELECT def AS upfirst_explicit FROM icu ORDER BY en COLLATE upperfirst;
SELECT def AS en_x_explicit FROM icu ORDER BY def COLLATE "en-x-icu";

• trying to replicate the above quoted command.
  
• So I don't know ICU_LOCALE 'en-u-kf-upper'  the u and the kf refer to?
  

Even I followed  https://unicode-org.github.io/icu/userguide/locale/#the-locale-concept

1.     Language code
2.     Script code
3.     Country code
4.     Variant code
5.     Keywords

So which website can I get the info about the "kf" and "u".

--

 I recommend David Deutsch's <<The Beginning of Infinity>>

  Jian