<html xmlns="http://www.w3.org/1999/xhtml" lang="en">
 <head>
  <title>document.getElementById('id') and invalid IDs</title>
  <script type="text/javascript">
   function find(id, s) {
     var x = document.getElementById(id);
     if (x) {
       x.firstChild.data = s;
     }
   }
   function test() {
     find('test[a]', 'FOUND');
     find('dup', '+');
     find('', 'FOUND');
     find(' ', 'FOUND');
   }
  </script>
 </head>
 <body onload="test()">
  <ol>
   <li>id="test[a]": <span id="test[a]">NOT FOUND</span></li>
   <li>id="dup": <span id="dup">-</span><span id="dup">-</span><span id="dup">-</span><span id="dup">-</span><span id="dup">-</span></li>
   <li>id="": <span id="">NOT FOUND</span></li>
   <li>id=" ": <span id=" ">NOT FOUND</span></li>
  </ol>
 </body>
</html>
