This indicates the setup priority of the detour LSP, with values from 0 (highest) to 7. A low numeric value here lets the detour preempt existing lower-priority LSPs for bandwidth if the path is congested when it is signaled, which matters because a detour that cannot actually grab resources during a real failure defeats the purpose of fast reroute. For example, setting this to 0 for a voice-carrying tunnel's detour ensures it can bump a priority-7 best-effort LSP off a shared link during a failover.