What does the imref3d function do?

I am trying to extract a mask from a dicom contour as shown in this example: https://uk.mathworks.com/help/images/ref/dicomcontours.createmask.html

However I don't understand the purpose of the imref3d function, what exactly is this function doing with the contour data? The documentation of the function didn't really clarify as to what exactly it was doing, saying that "An imref3d object stores the relationship between the intrinsic coordinates anchored to the columns, rows, and planes of a 3-D image and the spatial location of the same column, row, and plane locations in a world coordinate system."

From what I understand by intrinsic coordinates it means the indices of pixels in a matrix that represents the 3D volume, but why would this be needed for DICOM contour info?

Also, how did they determine the arguments of the imre3d function from the line

imref3d([128,128,50],xlim,ylim,zlim);

I'm quite unclear on what this function does in this example and in particular how it was determined that the argument should be "[128,128,50],xlim,ylim,zlim"

Any help appreciated