citext's regexp_matches() functions weren't documented, either.

doc/src/sgml/citext.sgml

@@ -124,6 +124,11 @@ SELECT * FROM users WHERE nick = 'Larry';
   </para>
 
   <itemizedlist>
+   <listitem>
+    <para>
+      <function>regexp_matches()</>
+    </para>
+   </listitem>
    <listitem>
     <para>
       <function>regexp_replace()</>