<!DOCTYPE html>
<html>

<title>Reference for: position:fixed should not be clipped by the subframe clip, but it should be clipped by the "clip" clip, and the "clip" clip should be moved by the subframe.</title>

<style>

body {
  margin: 0;
  height: 4000px;
}

.subframe {
  margin-top: 300px;
  width: 400px;
  height: 400px;
  overflow: auto;
}

.subframeScrolled {
  height: 800px;
}

.greenSquare {
  position: absolute;
  top: 150px;
  left: 100px;
  width: 200px;
  height: 200px;
  background: lime;
}

</style>

<div class="subframe">
  <div class="subframeScrolled"></div>
</div>

<div class="greenSquare"></div>

<script>

document.documentElement.scrollTop = 50;
document.querySelector('.subframe').scrollTop = 150;

</script>