[JS] How to add CDATA section to xml?

var tagRoot = new XML("<test>");  
tagRoot.FirstElem =  "First";   
tagRoot.SecondElem = "Second";   
alert(tagRoot);  

I want to add CDATA section to element like below.

<test>

     <FirstElem><![CDATA[First]]></FirstElem>

     <SecondElem>Second</SecondElem>

</test>

Please help me.

Thanks in advance.