<html lang="en">
<style>
  html {
    letter-spacing: var(--a);
    --a: 0ic;
  }
</style>
<script>
  if (window.testRunner)
    testRunner.dumpAsText();

  onload = () => {
    CSS.registerProperty({
      inherits: true,
      name: '--a',
      syntax: '<length>',
      initialValue: '0',
    });
  };
</script>
This test passes if it doesn't crash.
</html>
