[Zope] Methods in a Simple Class

Hi all, I have built a trivial ZClass : CD (from CDProduct, from the guides). I try to add a DTML Method "render_short". This method would render the CD Instance on one short line. My ZClass has simple attributes (artist : string, title : string, description : text) I would like to be able to write this simple "render_short" DTML method like : Artist : <dtml-var artist> Title : <dtml-var title> Descr : <dtml-var description fmt="structured-text" newline_to_br> But when I insert a <dtml_var myCDInstance> in my index_html, I got a exception : Error Type: KeyError Error Value: artist There is no typo in my code... How can I access to my ZClass instance attribute from inside its methods ? Please help me :) Olivier