xdg-decoration: "server prefers SSDs" != "SSDs mandatory"
This allows a client to get the current decoration state without causing any unwanted side-effects, such as enabling SSDs when they prefer CSDs. It also enables compositors to differentiate between preferring SSDs and enforcing SSDs. If SSDs are enforced, clients must acknowledge that SSDs are enabled to avoid their windows being clipped to the xdg_toplevel geometry.