Estimate Anchor Boxes From Training Data

Information from an article on Matlab's "Estimate Anchor Boxes From Training Data" topic: "A distance metric based on IoU is invariant to the size of boxes, unlike the Euclidean distance metric, which produces larger errors as the box sizes increase [1 ] ". From which item this information is taken is indicated with "[1]". However, this article numbered 1 has not been written. How can I learn from which article this information is taken? Thank you.