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chromium/third_party/blink/web_tests/svg/custom/pattern-within-other-pattern.html 

<!DOCTYPE html>
<svg width="100" height="100">
  <pattern id="outer" width="1" height="1">
    <pattern id="inner" width="1" height="1">
      <rect width="100" height="100" fill="url(#outer)"/>
    </pattern>
    <rect width="100" height="100" fill="green"/>
  </pattern>
  <rect width="100" height="100" fill="url(#inner)"/>
</svg>