Adding a menu entry to "Libraries"

Hi,

I know how to add a new Action to my Project popup menu, but I would like to add an Action to the "Libraries" node of a project to have for instance:

"Add xxx Library..." into it.

But I can't find this "Libraries" node (for which entries seems to be contextual ones) into my layer in context, so i can't figure out how to add an entry to it.

Could you help me on this?

Best,

J.