[Zope] Where does "field_" prefix come from in Formulator fields?

It appears that when expanding a Formulator form field a "field_" prefix gets tacked onto the field name. For example, one field I have is named "postal_code". When this <td tal:content="structure here/form/postal_code/render">item</td> is rendered it expands to <td><input size="10" value="" type="text" name="field_postal_code" /></td> although I named to the object "postal_code", not "field_postal_code". Where does "field_" come from and how can I get rid of it? Thanks, -- Skip Montanaro - skip@pobox.com http://www.mojam.com/ http://www.musi-cal.com/