Flash was the OG 2D indie game engine before Unity happened. Your assets went into library, movieclips were asset + code, themselves also part of library. You

Flash was the OG 2D indie game engine before Unity happened. Your assets went into library, movieclips were asset + code, themselves also part of library. You would script and combine those into higher level movieclips and those would be aware of each other by parent/children realationships. Those were prefabs before era of prefabs.