[Zope] adding a line to a property using DTML

It's the simple things that stump! Is it possible in DTML to easily add a line to a property of type 'lines' ? (I can do it using external methods but would rather not) ie something like: <!--#call "manage_addProperty('items', '', 'lines')"--> <!--#call "manage_changeProperties( items = items + 'something new' ) "--> keeps giving me "Error value: illegal argument type for built-in operation" Cheers, Martin