relation between A, [R|t] and Q

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In the documentation a 3D-point is multiplied by A and [R|t] to receive the coordninates on the image plane.

From stereoRectify one can receive a matrix Q. This matrix allows to receive 3D-points from image coordinates. How are Q and A, [R|t] related to each other ( I can't figure it out from the description of Q).