<p>This test places the caret before the 'b' in 'bar' and Delete.  Afterword, 'foobar' should be in the first paragraph and 'baz' should be in the second.</p>
<div contenteditable="true">
<div>foo</div>
<pre id="test">bar
baz</pre>
</div>

<script>
var s = window.getSelection();
var e = document.getElementById("test");
s.setPosition(e, 0);
document.execCommand("Delete");
</script>