Default environment properties for the entire scene (post-processing effects, lightning and background settings).
WorldEnvironment node is used to configure the default Environment for the scene.
WorldEnvironment allows the user to specify default lighting parameters (e.g. ambient lighting), various post-processing effects (e.g. SSAO, DOF, Tonemapping), and how to draw the background (e.g. solid color, skybox). Usually, these are added in order to improve the realism/color balance of the scene.