This read-write OCTET STRING, though its source description is empty, sits among the spanning tree group objects alongside stGroupAddr and stRootID and holds this bridge's own Bridge Identifier, combining priority and MAC address, used in the 802.1D spanning tree root-election algorithm. An administrator adjusts the priority portion to influence whether this bridge is favored to become the network's spanning tree root. For example, the admin lowers the priority encoded in stBridgeId so this ES/1 is preferred as spanning tree root over a less capable neighboring switch.