People got crazy with their art and literature after World War II. A period known as postmodernism (yep, it came after Modernism) was all about its experimental style. It's like the literary equivalent of putting Mentos in Diet Coke and seeing what happens. (Hint: something awesome. And messy.)
The Stanford Encyclopedia of Philosophy describes postmodernism as "a set of critical, strategic and rhetorical practices employing concepts such as difference, repetition, the trace, the simulacrum, and hyperreality to destabilize other concepts such as presence, identity, historical progress, epistemic certainty, and the univocity of meaning." That's academic speak for "quirky."
Postmodernism includes anything from William Faulkner to Dave Eggers. Watch:
Put a random blank page in the middle of your chapter? Postmodern.
Express your thoughts with a chart instead of words? Postmodern.
Write your entire book as comics? Postmodern.
But there's more to it than that. Almost too much more, actually. The Los Angeles Times shows us—with graphics! —that it's pretty tough to nail down the nutty world of postmodernism.
Bottom line: postmodernist literature is playful. With what? It varies. In what way? It varies. For what purpose? It varies. It's like a good wine—depends on the varietal.