<style>
head, script, span {
    display: block;
}
head {
    -webkit-user-modify: read-write-plaintext-only;
}
script::first-letter {
    --font-size-ch: 0;
}
</style>
<script>
    // <-- magic whitespace
onload = () => {
  document.querySelector('script').appendChild(document.createElement('span'));
  document.execCommand('FindString', false, 'a');
  document.execCommand('FontSizeDelta', false, '1');
};
if (window.testRunner)
    testRunner.dumpAsText();
</script>
<p>The test PASS if it does not CRASH.</p>