function bloc_b(bloc_id){
  var xhr=getXhr();

  xhr.onreadystatechange=function(){
    if(xhr.readyState==4 && xhr.status==200){
      var docXML=xhr.responseXML;

      var source=docXML.getElementsByTagName('source').item(0).firstChild.data;
      var destination=docXML.getElementsByTagName('destination').item(0).firstChild.data;

      var bloc_src_contenu=document.getElementById('bloc_'+source).innerHTML;
      document.getElementById('bloc_'+source).innerHTML=document.getElementById('bloc_'+destination).innerHTML;
      document.getElementById('bloc_'+destination).innerHTML=bloc_src_contenu;
    }
  }

  xhr.open("POST","blocs.php",true);
  xhr.setRequestHeader('Content-Type','application/x-www-form-urlencoded');

  xhr.send("sens=bas&bloc_id="+bloc_id);
}

function bloc_h(bloc_id){
  var xhr=getXhr();

  xhr.onreadystatechange=function(){
    if(xhr.readyState==4 && xhr.status==200){
      var docXML=xhr.responseXML;

      var source=docXML.getElementsByTagName('source').item(0).firstChild.data;
      var destination=docXML.getElementsByTagName('destination').item(0).firstChild.data;

      var bloc_src_contenu=document.getElementById('bloc_'+source).innerHTML;
      document.getElementById('bloc_'+source).innerHTML=document.getElementById('bloc_'+destination).innerHTML;
      document.getElementById('bloc_'+destination).innerHTML=bloc_src_contenu;
    }
  }

  xhr.open("POST","blocs.php",true);
  xhr.setRequestHeader('Content-Type','application/x-www-form-urlencoded');

  xhr.send("sens=haut&bloc_id="+bloc_id);
}