function showTab(id)
{
  // get all tabs by classname and close
  var tabs = document.getElementsByClassName('tab');
  for(i=0;i<tabs.length;i++){
    tabs[i].style.display='none';
  }
  document.getElementById(id).style.display='block';
}

function hideTab(id)
{
  document.getElementById(id).style.display='none';
}


document.getElementsByClassName = function (c) { 
  var r = new Array() 
  var j = 0 
  var o = document.getElementsByTagName("*") 
  for(i=0;i<o.length;i++){ 
    if(o[i].className == c){ 
      r[j]=o[i];j++; 
    } 
  } 
  return r; 
}