# File lib/mizuho/id_map.rb, line 212
                def <=>(other)
                        if (a = Utils.extract_chapter(title)) &&
                           (b = Utils.extract_chapter(other.title))
                                # Sort by chapter whenever possible.
                                a[0] = Utils.chapter_to_int_array(a[0])
                                b[0] = Utils.chapter_to_int_array(b[0])
                                return a <=> b
                        else
                                return title <=> other.title
                        end
                end