Returns a string representation of the XMLi element.
        @return: str

def to_string(self, indent="", newl="", addindent=""):
        '''
        Returns a string representation of the XMLi element.
        @return: str
        '''
        buf = StringIO()
        self.to_xml().writexml(buf, indent=indent, addindent=addindent,
                               newl=newl)
        return buf.getvalue()