Eyelid rig

Hi, I am analysing Sintel lite 2.57 rig, and currently trying to get some understanding of face rig. I am looking at eyelids now, and don’t understand why are there so many bones for it. I mostly see what is following what, but so many bones (mch, def, org, and then at least 2-3 more groups, that flower shape…). For some I don’t even see why are they there, because it looks like they aren’t constraining anything and don’t have any constraints on them. And only a few of them have drivers, and it looks to me they are controlling shape keys through actions with the sliders. Similar is for the mouth… I am familiar with most things for body rig, ik,fk,reverse pivot chain, and other, but this is unclear to me.
So if anyone could give me some kind of explanation about it, it would be appreciated.

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