about:blankに設定した後のiframeのsrcの詳細について

function clearIframe(id){
var el = document.getElementById(id),
iframe = el.contentWindow;
if(el){
el.src = 'about:blank';
try{
iframe.document.write('');
iframe.document.clear();
}catch(e){};
//The above will clear most of the memory and document node records
//Lastly delete the iframe and you're done.
document.body.removeChild(el);
} } clearIframe('iframe_id');