Clarify spacing in aviz (or lack thereof). (#4148)

Author: Crell

language/oop5/visibility.xml

@@ -164,6 +164,13 @@ $b->pubYear = 2023; // Fatal Error
       </simpara>
      </listitem>
     </itemizedlist>
+    <note>
+     <simpara>
+      Spaces are not allowed in the set-visibility declaration.
+      <literal>private(set)</literal> is correct.
+      <literal>private( set )</literal> is not correct and will result in a parse error.
+     </simpara>
+    </note>
     <simpara>
      When a class extends another, the child class may redefine
      any property that is not <literal>final</literal>.  When doing so,