Unlike the other series, Series Eleven contains only one world.
Its inhabitants are peculiar and unfriendly, and discourage visitors. Few people attempt to visit Series Eleven, fewer succeed, and none ever come back. (Almost none - see The Lives of Christopher Chant (spoilers).)
The people of Series Eleven all have powerful magic, possibly for similar reasons to the powerful magic of nine-lifed enchanters - after all, they have no otherworldly duplicates - but they have only one life each, and their magic is not exactly enchanter's magic, or indeed any form of magic understood in World 12A. They have complete control over the world around them - what the weather's like, what plants grow and where - which allows them to live an apparently low-tech life in the open forest. Food comes when they call, and they don't use fire at all (and look down on the other worlds for needing to). They are the inspiration for other worlds' legends of elves.
They have no laws as such - they go by pride and appearance and tradition. They admire absolute loyalty, especially when a person lies or cheats rather than be disloyal. They don't necessarily respect arrogance, but they don't respect anybody who isn't arrogant.
Furs and ornaments are signs of rank.
Their leader is the Dright. It is said that he is responsible for keeping Series Eleven down to a single world, in order that he have no rivals.