m2

(function(){

  var df1 = document.createDocumentFragment();
  df1.appendChild(document.createElement('A'));
  var df2 = document.createDocumentFragment();
  df2.appendChild(df1);

  alert(df1.firstChild && df1.firstChild.nodeName); // null
  alert(df2.firstChild && df2.firstChild.nodeName); // A

  var range = document.createRange();
  range.setStartBefore(df2.firstChild);
  range.setEndAfter(df2.lastChild);
  
  var df3 = range.extractContents();
  alert(df2.firstChild && df2.firstChild.nodeName); // null
  alert(df3.firstChild && df3.firstChild.nodeName); // A

  document.body.appendChild(df3);
  alert(df3.firstChild && df3.firstChild.nodeName); // null

})()

http://d.hatena.ne.jp/miya2000/