[Zope] - Referring to URL pieces within Z Publisher/DTML

[skip@calendar.com (Skip Montanaro)]

I'm using Z Publisher to publish an object and using DocumentTemplate to
render the results.  Things were working fine until I tried to build a URL
in the output.  My template currently contains

    <form action="<!--#var URL0-->" method=GET>

but I'm getting a KeyError:

    Traceback (innermost last):
      blah, blah, blah
      File /usr/local/lib/automatrix/python/showcal.py, line 184, in __call__
      File /home/dolphin/skip/src/Zope-1.9.0b3-src/lib/python/DocumentTemplate/DT_String.py, line 514, in __call__
	(Object: <string>)
    KeyError: URL0

The document template is defined as a class variable, template, and called
as

    return self.template(month=month, year=year, cal=cal, hint=hint,
                         REQUEST=REQUEST)

I've tried replacing <!--#var URL0--> with several different alternatives

    <!--#var SERVER_NAME-->
    <!--#var REQUEST['SERVER_NAME']-->
    <!--#var expr="REQUEST['URL0']"-->

but none worked.

What is available to me within a simple Z Publisher environment?  For now
I'm explicitly passing in a value, however the DTML documentation suggests
(http://www.digicool.com/site/Principia/DTML.html/DTML.html#41409) that URL0
and several other variables should be available.  Is this true only within
Zope?

Skip Montanaro	   | Mojam: "Uniting the World of Music" http://www.mojam.com/
skip@calendar.com  | Musi-Cal: http://concerts.calendar.com/
518-372-5583