Hi, I'm not sure if this is where I report typos/errors in the doc, but the IRC channel pointed me here.
As mentioned in one of the comments, the description for pygame.sprite.LayeredUpdates ( http://www.pygame.org/docs/ref/sprite.html#pygame.sprite.LayeredUpdates): "If the sprite you add has an attribute layer then that layer will be used." should read "If the sprite you add has an attribute '_layer' then that layer will be used."
