In role-playing games, a common method of arbitrating the capabilities of different characters is to assign each one to a character class. A character class aggregates several abilities and aptitudes, and may also sometimes detail aspects of background and social standing or impose behaviour restrictions. Classes may be considered to represent archetypes, or specific careers. RPG systems that employ character classes often subdivide them into levels of accomplishment, to be attained by players during the course of the game. It is common for a character to remain in the same class for its lifetime; although some games allow characters to change class, or attain multiple classes. Some systems eschew the use of classes and levels entirely; others hybridise them with skill-based systems or emulate them with character templates. Dungeons & Dragons (D&D), the first formalised roleplaying game, introduced the use of classes, and many subsequent games adopted variations of the same idea.These games are sometimes referred to as 'class-based' systems. As well as tabletop games, character classes are found in many computer role-playing games and live action role-playing games.