code: def to_string(self):
          
          buff = u""
          for child in self.content.iter():
              if child.tag in [self.qn('text:p'), self.qn('text:h')]:
                  buff += self.text_to_string(child) + "\n"
          # remove last newline char
          if buff:
              buff = buff[:-1]
          return buff
docs: Converts the document to a string.