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 fc4b95378715ec9a0faf5c98673a6ea8ac7a0ec1..91557f4fb0fabef26a0381c5c4a5d8b7d3282596 100644 (file)
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -3110,8 +3110,11 @@ SELECT NOT(ROW(table.*) IS NOT NULL) FROM TABLE; -- detect at least one null in
        </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>