<script>
function test()
{
    if (window.testRunner)
        testRunner.dumpAsText();
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    ta.focus();
    document.execCommand("InsertLineBreak");
    var result = ta.value;
    if (result == "\n")
        document.write("<p>Hooray, the test was successful!</p>");
    else
        document.write("<p>The test failed, result was '" + result.replace("\n", "\\n") + "'.</p>");
}
</script>
<body onload="test()">
<p><textarea id="ta"></textarea></p>