docs: def set_prefix(self, elt, pyobj):
          '''use this method to set the prefix of the QName,
          method looks in DOM to find prefix or set new prefix.
          This method must be called before get_formatted_content.
          '''
          if isinstance(pyobj, tuple):
              namespaceURI,localName = pyobj
              self.prefix = elt.getPrefix(namespaceURI)