SC 2.4.13 perimeter calculation inacuracy

Hi,

 

The calculation in the example does not meet the definition of the
perimeter:

 <https://www.w3.org/TR/WCAG22/#dfn-perimeter>
https://www.w3.org/TR/WCAG22/#dfn-perimeter

 

The definition says:

"continuous line forming the boundary of a shape *not including shared
pixels*, [.]"

 

But the example does not subtract the shared pixels (like it did in the
draft):

"The perimeter calculation for a 2 CSS pixel perimeter around a rectangle is
4h+4w, where h is the height and w is the width."

 

Is this inaccuracy an approximate value due to easier readability or do I
miss something?

 

Wolfgang