He means, of course
<c><</c>
A better example is:
<c><d/></c>
In SGML, if <c> has CDATA declared content, then the content of <c> is
the string "<d/>". In XML+CDATA, without a DTD, this is
indistinguishable from <c> containing an empty element <d>.
-Chris
-- <!NOTATION SGML.Geek PUBLIC "-//Anonymous//NOTATION SGML Geek//EN"> <!ENTITY crism PUBLIC "-//O'Reilly//NONSGML Christopher R. Maden//EN" "<URL>http://www.oreilly.com/people/staff/crism/ <TEL>+1.617.499.7487 <USMAIL>90 Sherman Street, Cambridge, MA 02140 USA" NDATA SGML.Geek>