diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 487bb103637..1cd281dd90b 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -1932,8 +1932,11 @@
        <entry><type>text</type></entry>
        <entry>
         Convert 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>.
        </entry>
        <entry><literal>initcap('hi THOMAS')</literal></entry>
        <entry><literal>Hi Thomas</literal></entry>