[Zope] Getting access to additional-passed in variables from dtml

Hello, I want to use dtml as a variable-substitution engine. However, I'm not sure how to see what variables I have available. For example, with page templates I can do the following: <span tal:repeat="key python:options.keys()"> <span tal:replace="key">The Key</span> </span> Is there an equivalent structure in dtml? Thanks, VanL