// show-hide tabs

function setClassname(id, classname){ document.getElementById(id).className = classname; }
function getClassname(id){ return document.getElementById(id).className; }
function replaceClassname(id, find, replace){ setClassname(id, getClassname(id).replace(new RegExp(find), replace)); }

function showTab(currentTab, newTab){
  replaceClassname(currentTab, 'visible', 'invisible');
  replaceClassname(newTab, 'invisible', 'visible');
}