Пример

/* ====== Select Code from phpBB3 to uCoz ~ http://allcity.net.ru/ ====== */    
  div.bbCodeName {margin-bottom:3px;}    
  div.codeMessage code {font-size:14px;}    
  /* ====================================================================== */

<script type="text/javascript">    
  // Select Code from phpBB3 to uCoz ~ http://allcity.net.ru/    
  function selectCode(a){    
  var e=a.parentNode.parentNode.getElementsByTagName('code')[0];    
  if(window.getSelection){    
  var s=window.getSelection();    
  if(s.setBaseAndExtent){    
  s.setBaseAndExtent(e,0,e,e.innerText.length-1);    
  }else{    
  var r=document.createRange();    
  r.selectNodeContents(e);    
  s.removeAllRanges();    
  s.addRange(r);}    
  }else if(document.getSelection){    
  var s=document.getSelection();    
  var r=document.createRange();    
  r.selectNodeContents(e);    
  s.removeAllRanges();    
  s.addRange(r);    
  }else if(document.selection){    
  var r=document.body.createTextRange();    
  r.moveToElementText(e);    
  r.select();}}    
  // Замена Code на Выделить всё...    
  codediv=document.getElementsByTagName('div');    
  for(i=0;i<codediv.length;i++){    
  if(codediv[i].className=="bbCodeBlock"){    
  s=codediv[i].innerHTML;    
  s=s.replace(/>Code</g,'>Код: <a href="#" onclick="selectCode(this);return false;">Выделить всё<\/a><').replace('<!--uzc-->','<!--uzc--><code>').replace('<!--\/uzc-->','<\/code><!--\/uzc-->');    
  codediv[i].innerHTML=s;}}    
  </script>