function hide(id)
{
  document.getElementById(id).style.visibility = "hidden";
}

function show(id)
{
  document.getElementById(id).style.visibility = "visible";
}

function changevisibility(id)
{
  if (document.getElementById(id).style.visibility != "visible")
  {
    document.getElementById(id).style.visibility = "visible";
  }
  else
  {
    document.getElementById(id).style.visibility = "hidden";
  }
}


function pagecentered(id)
{

  document.getElementById(id).style.top = (document.documentElement.offsetHeight/2)-(document.getElementById(id).offsetHeight/2)+'px';
  document.getElementById(id).style.left = (document.documentElement.offsetWidth/2)-(document.getElementById(id).offsetWidth/2)+'px';

}