<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100">
  <defs>
    <pattern id="green" x="0" y="0" width="100" height="100">
      <rect x="0" y="0" width="100" height="100" fill="green"/>
    </pattern>
  </defs>
  <rect x="0" y="0" width="100" height="100" fill="red" />
  <rect x="0" y="0" width="100" height="100" fill="url(#green)" />
</svg>