The game of chess is commonly divided into three phases: the opening, middlegame, and endgame. There is a large body of theory regarding how the game should be played in each of these phases, especially the opening and endgame. Those who write about chess theory, who are often but not necessarily also eminent players, are referred to as ""theorists"" or ""theoreticians"".""Opening theory"" commonly refers to consensus, broadly represented by current literature on the openings. ""Endgame theory"" consists of statements regarding specific positions, or positions of a similar type, though there are few universally applicable principles. ""Middlegame theory"" often refers to maxims or principles applicable to the middlegame. The modern trend, however, is to assign paramount importance to analysis of the specific position at hand rather than to general principles.The development of theory in all of these areas has been assisted by the vast literature on the game. In 1913, preeminent chess historian H.J.R. Murray wrote in his 900-page magnum opus A History of Chessthat, ""The game possesses a literature which in contents probably exceeds that of all other games combined."" He estimated that at that time the ""total number of books on chess, chess magazines, and newspapers devoting space regularly to the game probably exceeds 5,000"". In 1949, B. H. Wood opined that the number had increased to about 20,000. David Hooper and Kenneth Whyld wrote in 1992 that, ""Since then there has been a steady increase year by year of the number of new chess publications. No one knows how many have been printed..."" The world's largest chess library, the John G. White Collection at the Cleveland Public Library, contains over 32,000 chess books and serials, including over 6,000 bound volumes of chess periodicals. Chess players today also avail themselves of computer-based sources of information.