Don't give a poor example of letting special characters slip

into text cut'n'pasted to a <pre> HTML element.  Warn readers
that such characters are likely to appear in plain-text sources
often used to copy pre-formatted text from.

en_US.ISO8859-1/books/fdp-primer/sgml-markup/chapter.sgml

@@ -332,11 +332,22 @@
   There is a new copy of my primer for contributors to the FreeBSD
   Documentation Project available at
 
-    <URL:http://people.FreeBSD.org/~nik/primer/index.html>
+    &lt;URL:http://people.FreeBSD.org/~nik/primer/index.html&gt;
 
   Comments appreciated.
 
   N</pre>]]></programlisting>
+
+	  <para>Keep in mind that <literal>&lt;</literal> and
+	    <literal>&amp;</literal> still are recognized as special
+	    characters in pre-formatted text.  This is why the example
+	    shown had to use <literal>&amp;lt;</literal> instead of
+	    <literal>&lt;</literal>.  For consistency,
+	    <literal>&amp;gt;</literal> was used in place of
+	    <literal>&gt;</literal>, too.  Watch out for the special characters
+	    that may appear in text copied from a plain-text source,
+	    e.g., an e-mail message or program code.</para>
+
 	</example>
       </sect3>