Flush valves on the drinking supply or on a shared tank have integral back-siphonage protection that is protected from interference, are compatible with the fixture, fed by at least DN 25 hydraulically sized pipe, have the outlet at a set height above the pan rim, are used only where pressure and flow suffice without affecting other appliances, and have a stop valve on the branch (2003 text).
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.