Simple links do reside in the document from which they start.
Unlike simple links, extended links need not be located at any of the locations connected by the link. They will, however, be located somewhere. Some people whose judgment I trust assure me there is no consensus on this issue and that it will therefore be left to the implementation to decide what to do. Just like HTML, more or less. Depending on what the conformance clause of the spec says in the end, some of these may not be correct implementations, but for now they are at least all imaginable.