How do you adopt the AVAudioMixing Protocol for a custom AVAudioUnitNode?

Does anyone know how one adopts the AVAudioMixing Protocol when building a custom AVAudioUnit node?

Like documentation, or better yet an example show what needs to be done?

I am a little confused, because the documentation reads that an custon node has to adopt it so a

AVAudioMixerNode

AVAudioEnvironmentNode downstream to respond to it.

But I dont' understand when you fill in the AVAudioMixing protocol stub with? Are you telling your custom node to do something, or are you telling the AVAudioMixerNode and AVAudioEnviromentNodes downstream to do something (makes more sense)? But being a protocol that implies that a delegate is being used from the AVAudioMixerNode and AVAudioEnviromentNodes, and I don't get how one gets a referrence to that.

Thanks in Advances.

Staque