[Zope] code problem

Fri Oct 10 20:26:43 EDT 2003

I am new to zope web application I want to creat a tab interface
I copy following code form somebody else

<html metal:use-macro="container/standard_template.pt/macros/page">
  <div metal:fill-slot="body">
      <table width="100%" cellpadding="0" cellspacing="0"
              tal:define="username user/getUserName;
	                          selectedTab request/tab>
      </table>
       </div>
</html>

When i test it I get 

Zope Error
Zope has encountered an error while publishing this resource.

Error Type: KeyError
Error Value: tab

How can i fix this problem?

Thanks