In the case of comic books, an annual is considered a separate series for purposes of numbering and collectibility; a particular periodical's "Annual" will thus have its own numbering series, or alternately be referred to by the year of its publication (such as "The Amazing Spider-Man '99 Annual"). A comic book annual customarily has a larger page count than its monthly counterpart, leaving room for longer single stories, multiple stories in a single annual and/or "extra" material that the monthly series lacks the space to publish. These "extras" may include biographical information on featured characters, full-page pin-ups of characters, reprints of previously published material, or all-new short stories (often called "back-up" stories). An annual as a whole was once considered an "extra" in itself, providing story material in addition to the customary 12 issues per year of a monthly series.