doc: Better example for custom ICU rules

Use a more practical example, and also add some explanation.

Reported-by: Jeff Davis 

diff --git a/doc/src/sgml/ref/create_collation.sgml b/doc/src/sgml/ref/create_collation.sgml
index 289f8147f14730eab108739c8c0a806b0fb2f363..f6353da5c15c17a5fb2ccccc684273c81f84c88f 100644 (file)
--- a/doc/src/sgml/ref/create_collation.sgml
+++ b/doc/src/sgml/ref/create_collation.sgml
@@ -243,11 +243,17 @@ CREATE COLLATION german_phonebook (provider = icu, locale = 'de-u-co-phonebk');
   
 
   
-   To create a collation using the ICU provider, based on the English ICU
-   locale, with custom rules:
+   To create a collation using the ICU provider, based on the root ICU locale,
+   with custom rules:
 
-en_custom (provider = icu, locale = 'en', rules = '&a < g');]]>
+custom (provider = icu, locale = 'und', rules = '&V << w <<< W');]]>
 
+   With this rule, the letter W is sorted after
+   V, but is treated as a secondary difference similar to an
+   accent.  Rules like this are contained in the locale definitions of some
+   languages.  (Of course, if a locale definition already contains the desired
+   rules, then they don't need to be specified again explicitly.)  See the ICU
+   documentation for further details and examples on the rules syntax.