208 Already Reported
Told you about that one — the code that avoids repeating a resource inside a 207.
RFC 5842 gave WebDAV bindings: the same resource reachable by two paths. In a deep listing this would enumerate the same subtree twice — unless the second report just says 208: already reported this one, look above.
It almost never opens a response: it lives inside the XML body of a 207, as the status of a repeated member. It is one of the least seen codes in the whole registry — a specimen that only exists inside another.
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
... <D:status>HTTP/1.1 208 Already Reported</D:status> ...