再请教一个js语句

L@_@K
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title> new document </title>
    <meta name="generator" content="editplus" />
    <meta name="author" content="Gao YiXiang" />
    <meta name="email" content="[email protected]" />
    <meta name="keywords" content="javascript dhtml dom" />
    <meta name="description" content="I love web development." />
</head>
<body>    <textarea id="ttaTarget" rows="5" cols="20">ab123
abc
1uyt</textarea>    <select id="sltTest">
        <option value="" selected="selected">-- Please Select --</option>
        <option value="abcde">abcde</option>
    </select>
<script type="text/javascript">
<!--
var oSlt = document.getElementById("sltTest");
oSlt.onchange = function()
{
    if (this.value != "")
    {
        var oTta = document.getElementById("ttaTarget");
        oTta.value += "\n" + this.value;
    }
};
//-->
</script>
</body>
</html>