I see the ISketchBlockDefinition and ISketchBlockInstance interfaces that one can use to get information about blocks including gettings Arcs, Lines, ect. What about when there is a block inside a block? I do not see anywhere in the API on getting blocks inside blocks.

I know that I can make blocks nested. Here is an example in a feature tree:

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Using the API how can we tell is a block is inside a block? I would expect it to be in the block definition interface?