The expression shifts the enlarged layer as if it were under a “virtual magnifying glass”.
Unlike the standard Magnify effect, which converts any image to bitmap, this option will preserve the 100% quality of the enlarged image.

Applies to the Position parameter.

mag = thisComp.layer("Center"); // Layer, which will be as magnifiers center
big = thisLayer;
bigS = transform.scale;
small = thisComp;
ratioW = (big.width/(100/bigS[0]))/small.width;
ratioH = (big.height/(100/bigS[1]))/small.height;
p = mag.toComp([0,0])-[thisComp.width,thisComp.height]/2;
value-[p[0]*ratioW,p[1]*ratioH]+p