clip-path

<svg viewBox="0 0 20 20" xmlns="http://www.w3.org/2000/svg">
  <clipPath id="myClip" clipPathUnits="objectBoundingBox">
    <circle cx=".5" cy=".5" r=".5" />
  </clipPath>

  <!-- Top-left: Apply a custom defined clipping path -->
  <rect
    x="1"
    y="1"
    width="8"
    height="8"
    stroke="green"
    clip-path="url(#myClip)" />

  <!-- Top-right: Apply a CSS basic shape on a fill-box
       geometry. This is the same as having a custom clipping
       path with a clipPathUnits set to objectBoundingBox -->
  <rect
    x="11"
    y="1"
    width="8"
    height="8"
    stroke="green"
    clip-path="circle() fill-box" />

  <!-- Bottom-left -->
  <rect
    x="1"
    y="11"
    width="8"
    height="8"
    stroke="green"
    clip-path="circle() stroke-box" />

  <!-- Bottom-right: Apply a CSS basic shape on a view-box
       geometry. This is the same as having a custom clipping
       path with a clipPathUnits set to userSpaceOnUse -->
  <rect
    x="11"
    y="11"
    width="8"
    height="8"
    stroke="green"
    clip-path="circle() view-box" />
</svg>