function get_by_id( id )
{
  return( document.getElementById ? document.getElementById( id ) :
  document.all ? document.all[ id ] : 0 );
};

function toggle_visibility( id )
{
  var element = get_by_id( id );
  if (!element) return( false );
  
  if (element.style.display == 'none')
  {
    element.style.display = 'block';
  }
  else
  {
    element.style.display = 'none';
  }
  return( id );
}

function displayproductpage( id )
{
  //alert("A toto napsal JavaScript");
  
  list = new Array("info", "requirements", "download", "purchase", "changes", "licence");
  
  for (i=0; i<list.length; i++)
  {
    var name = list[i];
    var element = get_by_id("page" + name);
    var button = get_by_id("menu" + name);
    if (!element || !button) continue;
    
    if (name == id)
    {
      element.style.display = 'block';
      button.className = 'itemselected';
    }
    else
    {
      element.style.display = 'none';
      button.className = 'item';
    };
  };
}