Information taken from the "Star Trek Encyclopedia" and "Star Trek Chronology" is mostly accepted on Memory Alpha as well, to the extent that it does not break from established on-screen facts. Content from these sources is an acknowledged grey area of Memory Alpha's canon policy and is disregarded if deemed speculative or contradictory. Thus, in some ways they hold the same weight as novels and other publications do for Star Wars canon: a "second tier" of canonicity, which is subservient to primary (on-screen) sources.