def METHOD_NAME(self, index, title):
    """Sets the title of a container page.
    Parameters
    ----------
    index : int
        Index of the container page
    title : unicode
        New title
    """
    titles = list(self.titles)
    # for backwards compatibility with ipywidgets 7.x
    if title is None:
        title = ''
    titles[index]=title
    self.titles = tuple(titles)