def add_bookmark(self, name, time, chan=''):
        """Add a new bookmark

        Parameters
        ----------
        name : str
            name of the bookmark
        time : (float, float)
            float with start and end time in s

        Raises
        ------
        IndexError
            When there is no selected rater
        """
        try:
            bookmarks = self.rater.find('bookmarks')
        except AttributeError:
            raise IndexError('You need to have at least one rater')
        new_bookmark = SubElement(bookmarks, 'bookmark')
        bookmark_name = SubElement(new_bookmark, 'bookmark_name')
        bookmark_name.text = name
        bookmark_time = SubElement(new_bookmark, 'bookmark_start')
        bookmark_time.text = str(time[0])
        bookmark_time = SubElement(new_bookmark, 'bookmark_end')
        bookmark_time.text = str(time[1])

        if isinstance(chan, (tuple, list)):
            chan = ', '.join(chan)
        event_chan = SubElement(new_bookmark, 'bookmark_chan')
        event_chan.text = chan

        self.save()
Add a new bookmark

        Parameters
        ----------
        name : str
            name of the bookmark
        time : (float, float)
            float with start and end time in s

        Raises
        ------
        IndexError
            When there is no selected rater