function getElementsByClassName(cl, el) {
var retnode = [];
var myclass = new RegExp('\\b'+cl+'\\b');
var elem = el.getElementsByTagName('*');
for (var i = 0; i < elem.length; i++) {
var classes = elem[i].className;
if (myclass.test(classes)) retnode.push(elem[i]);
}
return retnode;
};

function showTab(tab, tabs_box, item) {
  var tabs_el = document.getElementById(tabs_box);
  var tabs_panel = getElementsByClassName('tabs_panel', tabs_el);
  var tabs_items = getElementsByClassName('tabs_items', tabs_el);
  var items = getElementsByClassName('tab_item', tabs_items[0]);
  for (var i = 0; i < items.length; i++) {
    items[i].className = items[i].id==item?'tab_item':'tab_item hidden';
  }
  var tabs = getElementsByClassName('tab', tabs_panel[0]);
  for (var i = 0; i < tabs.length; i++) {
    tabs[i].className = tabs[i]==tab?'tab tab_selected':'tab';
  }
}