For X to pertain particularly to postmodernism involves the compounding or modifying of older usages into events which are "new" if only in the circumstances of their use. Through the early twentieth century X is most often a place-holder for an unknown quantity, or an allusion to facts unknown or hidden, incorrect or prohibited. In the 1980s and 1990s these uses have expanded into popular contexts from the old enclaves of science and risqu art. They represent a shift from an allusion to something unknown, to the illusion of something unknowable. X then becomes a pointer to a meaning that can no longer be named, nor could have been named in the first place. Its combination of the unknown and unknowable enjoy refuge in the distinct stylishness of indeterminacy, regress and mysticism.