Clarify documentation for the initcap function

This commit documents differences in the definition of word separators for
the initcap function between libc and ICU locale providers.
Backpatch to all supported branches.

Discussion: https://postgr.es/m/804cc10ef95d4d3b298e76b181fd9437%40postgrespro.ru
Author: Oleg Tselebrovskiy <o.tselebrovskiy@postgrespro.ru>
Backpatch-through: 13

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 8fbef434f3687f9a0989e1d55e886cef6c29f437..f9b23ac7a82eebec2ca3ce25a17b3ce9d9a52557 100644 (file)
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -2879,8 +2879,11 @@ repeat('Pg', 4) <returnvalue>PgPgPgPg</returnvalue>
        </para>
        <para>
         Converts the first letter of each word to upper case and the
-        rest to lower case. Words are sequences of alphanumeric
-        characters separated by non-alphanumeric characters.
+        rest to lower case. When using the <literal>libc</literal> locale
+        provider, words are sequences of alphanumeric characters separated
+        by non-alphanumeric characters; when using the ICU locale provider,
+        words are separated according to
+        <ulink url="https://www.unicode.org/reports/tr29/#Word_Boundaries">Unicode Standard Annex #29</ulink>.
        </para>
        <para>
         <literal>initcap('hi THOMAS')</literal>