function collapse(id)
{
  obj_id = id + '_childs';
  obj = document.getElementById(obj_id);
  if(!obj)
    return;

  obj.style.display = "none";

  plus = document.getElementById(id + '_plus');
  if(!plus)
    return;

  plus.style.display = "block";

  minus = document.getElementById(id + '_minus');
  if(!minus)
    return;

  minus.style.display = "none";
}

function expand(id)
{
  obj_id = id + '_childs';
  obj = document.getElementById(obj_id);
  if(!obj)
    return;

  obj.style.display = "block";

  plus = document.getElementById(id + '_plus');
  if(!plus)
    return;

  plus.style.display = "none";

  minus = document.getElementById(id + '_minus');
  if(!minus)
    return;

  minus.style.display = "block";
}