XHTML hell

 1: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
 2:      "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"
 3: [
 4:   <!ENTITY hello "Parser <b>nightmare</b>">
 5:   <!ENTITY % xx '&#37;zz;'>
 6:   <!ENTITY % zz '&#60;!ENTITY tricky "error-prone" >' >
 7:   %xx;
 8: ]>
 9: 
10: <html xmlns="http://www.w3.org/1999/xhtml">
11:     <head>
12:         <title>Simple XHTML document</title>
13:     </head>
14: 
15:     <body>
16:         <p>This sample shows a &tricky; method.</p>
19:     </body>
20: </html>