CSS Masking: Basic shape using border-box should use stroke-box The spec states: "For SVG elements without an associated CSS layout box, the used value for ... border-box and margin-box is stroke-box." In this testcase, border-box is specified, so the clip-path of "inset(0) border-box" should be equivalent to "inset(0) stroke-box", and should not clip out the stroke. You should see a 100x100 green square formed by a stroked rect.