[Zope] Simple DTML date-stamp

[William BC Crandall]

Just starting to set things up, and I would like a 
standard_html_footer with a date-stamp.

As a start, I tried:

<hr>
<p>Last modified: <dtml-var name="date" fmt="aCommonZ"></p>
<p><dtml-var ZopeAttributionButton></p>
</body>
</html>

Why does this break?
Minimal format breaks in the same way:

<hr>
<p>Last modified: <dtml-var date fmt=aCommonZ></p>
<p><dtml-var ZopeAttributionButton></p>
</body>
</html>


In either case, View generates:

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

KeyError

Sorry, a Zope error occurred.

Traceback (innermost last):
  File C:\Program Files\TotipotentZope\lib\python\ZPublisher\Publish.py,
line 222, in publish_module
  File C:\Program Files\TotipotentZope\lib\python\ZPublisher\Publish.py,
line 187, in publish
  File C:\Program Files\TotipotentZope\lib\python\Zope\__init__.py, line
221, in zpublisher_exception_hook
    (Object: ApplicationDefaultPermissions)
  File C:\Program Files\TotipotentZope\lib\python\ZPublisher\Publish.py,
line 171, in publish
  File C:\Program Files\TotipotentZope\lib\python\ZPublisher\mapply.py,
line 160, in mapply
    (Object: standard_html_footer)
  File C:\Program Files\TotipotentZope\lib\python\ZPublisher\Publish.py,
line 112, in call_object
    (Object: standard_html_footer)
  File C:\Program Files\TotipotentZope\lib\python\OFS\DTMLMethod.py,
line 167, in __call__
    (Object: standard_html_footer)
  File C:\Program
Files\TotipotentZope\lib\python\DocumentTemplate\DT_String.py, line 502,
in __call__
    (Object: standard_html_footer)
  File C:\Program
Files\TotipotentZope\lib\python\DocumentTemplate\DT_Var.py, line 276, in
render
    (Object: date)
KeyError: date