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<iframe id='myFrame' />

 var src = 'data:text/html;charset=utf-8,' + encodeURIComponent(
          "<!doctype html><html><head></head><body><h1>Title</h1></body></html>");

 $('#myFrame').attr('src', src);

$('#myFrame').contents().find('html').html('new template');

var source =  "<!doctype html><html><head></head><body><h1>Title</h1></body></html>";

 $('#myFrame').contents().find('html').html(source);
 $('#myFrame').contents().find('html').html('<body>Hi2</body>');