cr:7.2.2b

If the attack is an attack-proxy, the attack and its attack-source move onto the combat chain as the chain link. The attack-proxy is the active-attack and the attack-source becomes attacking. If the attack-source was on a previous chain link, the attack-proxy on that chain link ceases to exist.[1.4.3c]

Example: Bone Basher is a one-handed weapon with an attack activated ability. After an attack-proxy of Bone Basher resolves, the attack-proxy and Bone Basher move onto the combat chain as a chain link, and the attack-proxy is considered the active-attack.