Detect single mini chessboards

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I'm in a situation where I need to detect separate mini chessboards (2 black squares 2 white squares). I was searching inside the source code for the function doing this kind of detection but I couldn't find it. Can somebody give me a hint?

And I also was wondering if the function findChessboardCorners() just finds these points where two black squares are intersecting or if it also runs some optimization algorithm to force the points to form parallel lines.