[Zope] index_html method in a zclass

Hi! Hope someone can help me out here. I've just created a simple zclass that contains an index_html method. I've also created a test instance of the class. I tought calling the instance using '<!--#var instancename-->' from a dtml method or document would render the class' index_html method, but I get no output. The only way I can display the instance' index_html is by dooing: '<!--#with instancename--><!--#var index_html--><!--#/with-->' Am I doing something wrong, or is the first method described in here not possible? Thanks in advance Sture Lygren