def set_title(self, index, title):
        """Sets the title of a container page.

        Parameters
        ----------
        index : int
            Index of the container page
        title : unicode
            New title
        """
        # JSON dictionaries have string keys, so we convert index to a string
        index = unicode_type(int(index))
        self._titles[index] = title
        self.send_state('_titles')