[Zope] Create my own edit form

Hi community, I'm trying to build my own edit form for DTML-Documents. Therefore I need to get the unrendered data of a document to print out in a textarea-box. How can I do that? I tried something like <textarea name="data:string" cols="50" rows="10"> <dtml-var "_[mydocument]"> </textarea> The variable 'mydocument' is the document I want to edit. But this returns the rendered dtml-code, only html-tag stay as they were. Who can help me? Thanks in advance Marc