<!DOCTYPE html>
<html>
<body>
<script>
function doe(aEl) {
aEl.style.display = '';
var doc = aEl.contentDocument;
doc.designMode = 'on';
try {
doc.execCommand("insertHTML",false,'some text');
} catch(e) {
document.getElementById('result').innerHTML = e;
}
}
</script>
<iframe onload="doe(this)" style="display:none"></iframe><br>
<pre id="result" style="background-color: red; width: 300px; white-space: -moz-pre-wrap;"></pre>
</body>
</html>