iframe的designmode属性

< html >
< head >
</ head >
<script language="javascript">
<!--
function start()
{
    document.getElementById("myiframe").contentWindow.document.designMode="on";
}
-->
</script>
< body onLoad="start()">
     < iframe id = " myiframe "  style = " width:750px; height:400px; border:1; " ></ iframe >
</ body >
</ html >