Sholes and Glidden typewriter length. The redesigned platen also introduced the modern spacing functionality (horizontal and axial movement providing letter and line spacing, respectively). The cylindrical platen became "an indispensable part of every standard [typewriter]". By the end of 1872, the appearance and function of the typewriter had assumed the form that would become standard in the industry and remain largely unchanged for the next century. Although the machine possessed a cylindrical platen and what was essentially a QWERTY keyboard, two design elements that would later become essential were lacking: the ability to write in upper and lowercase letters and "visible" print. Although the
Typewriter in the Sky and Fantasy: Themes, Works, and Wonders" (2005), Gary Westfahl commented, "Recursive fantasy fiction – that is, a fantasy about writing fantasy – is scarce. Luigi Pirandello's play "Six Characters in Search of an Author" (1921) offered a non-genre model." Westfahl noted that Hubbard's book was "an early genre example, perhaps inspired by Pirandello". Umberto Rossi wrote in "The Twisted Worlds of Philip K. Dick" (2011) that "Typewriter in the Sky" included a game in the form of metafiction within its plot development. "Typewriter in the Sky" is well regarded within the genre of fantasy; author David Wingrove noted in "The