how can I pre-compose layers via AEGP?

Thank you. But still, nothing works. I have no idea why.
I try to open a pre-composition I have just built and added to my main composition.
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Here's my source code:

AEGP_Collection2H collection = NULL;
AEGP_CollectionItemV2 coll_item;
coll_item.u.layer.layerH = temp_layerH;
ERR(suites.CollectionSuite2()->AEGP_NewCollection(globP->my_id, &collection));
ERR(suites.CollectionSuite2()->AEGP_CollectionPushBack(collection, &coll_item));
ERR(suites.CompSuite5()->AEGP_SetSelection(main_compH, collection));
ERR(suites.CommandSuite1()->AEGP_DoCommand(3061)); //3061 = open selection
ERR(suites.CollectionSuite2()->AEGP_DisposeCollection(collection));
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Where am I wrong? When I debug, every single line of code is done, but nothing seems to happen.

Call AEGP_SetSelection() to alert AE of the change.

How do I use these Collections?

I build a new collection, I build a collection item, I set item.u.layer.layerH at a layer I want to select and do collectionPushBack, then doCommand and after that disposeCollection. Nothing happens, and I don't even see how to tell the command which layer(s) it is referring to. Help!

Oh yeah...set the selection using AEGP_CollectionSuite.

You could set the current selection to the comps & layers to be pre-comped, then use AEGP_DoCommand (2071). 2071 == pre-compose.