function show_tab(tab_button){
  var t_div = xGetElementById(tab_button);
  var tab_divs = xGetElementsByClassName("tab-content-box");
  var em_len = tab_divs.length;

  for(var x=0; x < em_len; x++){
      tab_divs[x].style.display = "none";
      }

  t_div.style.display = "block";
  }