chromium/third_party/blink/web_tests/editing/selection/5099303.html

<p>This tests extending an editable selection across non-editable content.  Everything in the region below should be selected.</p>
<div id="div" contenteditable="true">x<span contenteditable="false">xx</span>x</div>

<script>
var sel = window.getSelection();
var div = document.getElementById("div");
sel.collapse(div, 0);
sel.modify("extend", "forward", "character");
sel.modify("extend", "forward", "character");
sel.modify("extend", "forward", "character");
</script>