than two months after the 'newest' issue is sold. And [...] not only recent material but a great deal of older material is finally being collected into trades". In 2015, Polygon highlighted that "though this was far less common a decade ago, pretty much every monthly comic out there right now is eventually collected into trade paperback or hardcover edition that prints several issues in one package". Trade paperbacks are often even given volume numbers, making them a serialization of sorts. Due to this, many writers now consider their plots with the trade paperback edition in mind, scripting stories that last four to twelve issues, which could easily be read as a "graphic novel." In addition, the publishing format has gained such respectability as literature that it became an increasingly prominent part of both book stores and public library collections. Trade paperbacks and graphic novels are the preferred format for circulating library collections, since these collections are created to be read, and not to be retained as collector's items or as investments. Attempts to catalogue and circulate single-issue comics can pose difficult problems and the durability of the trade paperback format is an important consideration for longevity and collection development in public and school libraries. Trade paperbacks "are also the primary culprit in people's confusion of the lexicon, since 'TPBs make up 95% of what many librarians refer to as graphic novels'". Despite the growing popularity of the trade paperback, the serialized, individual issues are still considered the primary mode of sale by comics publishers, and a poorly selling series may face cancellation irrespective of trade paperback sales. However, some series "survive on the popularity of their trades sales, not just in the direct market and local comic shops, but in book stores across the world" and at "Scholastic [book] fairs and the like". The popularity of trade paperbacks has resulted in older material being reprinted as well. The Essential Marvel line of trade paperbacks has reprinted heroes such as Spider-Man and the Fantastic Four and has been able to introduce these Silver Age stories to a new generation of fans. These editions tend to resemble a phone book in that these are very thick books and are black-and-white (to help keep the cost down). DC Comics has followed suit by introducing a line called Showcase Presents. The first four have included Superman, Green Lantern, Jonah Hex, and Metamorpho the