MPF's API reference is broken into several categories. All of it is presented in the way that the modules and classes are actually used in MPF.
MPF core components.
MPF devices, including physical devices like flippers, ball devices, switches, lights, etc. as well as logical devices like ball saves, extra balls, multiballs, etc.
Built-in modes, such as game, attract, tilt, credits, etc.
Hardware platforms interfacess for all supported hardware.
Modules responsible for all config players (show_player, light_player, score_player, etc.)
All unit test base classes for writing tests for MPF and your own game.
Things that don't fit into other categories, including utility functions, the base classes for modes, players, timers, and other utility functions.