Add note to properties for XMLDocument

Author: nielsdos

reference/dom/dom/dom-xmldocument.xml

@@ -82,6 +82,14 @@
 
   <section xml:id="dom-xmldocument.props">
    &reftitle.properties;
+   <note>
+    <simpara>
+     While the <classname>DOMDocument</classname> class allows setting certain
+     properties to influence parser behaviour, this class only uses the
+     <constant>LIBXML_<replaceable>*</replaceable></constant> constants to
+     configure the parser.
+    </simpara>
+   </note>
    <variablelist>
     <varlistentry xml:id="dom-xmldocument.props.xmlencoding">
      <xi:include xpointer="xmlns(db=http://docbook.org/ns/docbook) xpointer(id('domdocument.props.xmlencoding')/*)">