@dbDavid Bushell ☕
James's post, now on the Vispero site, explains why width and hight 1px aren't sufficient and how clip-path helps but it doesn't explain why clip-path alone is not sufficient.

I did some brief testing of the Vispero rule vs. the one @anatudorAna Tudor 🐯 proposed. In Safari, the focus ring is still around where the visually hidden text would be.

It's not uncommon for Safari's focus ring to be a little squirrelly; even the focus ring around the traditional utility class isn't the expected shape.