insertion-in-first-line-9.html

Enable keyboard shortcuts

<!DOCTYPE html>

<style>

  div { color: red; }

  div::first-line { color: green }

  #y { display: inline-block; }

</style>

<div id="x"><span id="y">This should be </span></div>

<script>

  x.offsetWidth;

  y.appendChild(document.createTextNode('green'));

</script>