Other examples include the availability of a sandbox mode without predefined goals or progression. The division of game content in stages or chapters, where each stage expands the rules that a player can use with respect to the previous stage, increases game complexity, and variety. If the game advances through these stages by moving through different areas, these areas are called levels or maps; if the character unlocks new abilities through activities or rewards, they receive a currency called experience points. These points can be used to upgrade or augment various pre-determined abilities.