var activeClassName = 'kasten active';
var disabledClassName = 'kasten';
var activeLiClassName = 'active';
var disabledLiClassName = '';

function showTab(tabClicked, tabId) {
  var tabToShow = document.getElementById(tabId);
  var tabClickedParent = tabClicked.parentNode;
  
  if (tabToShow != null) {
    // search the current active tab
    var allTables = document.getElementsByTagName('table');
    
    for (var i = 0; i < allTables.length; i++) {
      // active tab found
      if (allTables[i].className == activeClassName) {
        allTables[i].className = disabledClassName;
      }
    }
    
    // show the contents of the new tab
    tabToShow.className = activeClassName;
    
    // disable the old tab
    var allLis = document.getElementsByTagName('li');
    
    for (var i = 0; i < allLis.length; i++) {
      if (allLis[i].className == activeLiClassName) {
        allLis[i].className = disabledLiClassName;
      }
    }
    
    // activate clicked tab
    tabClickedParent.className = activeLiClassName;
  }
}