function $(v) {return document.getElementById(v) }
String.prototype.isEmpty = function() { return this.length==0 }
String.prototype.isEmail = function() { return /^([a-zA-Z0-9\_\-\.]+)\@([a-zA-Z0-9\_\-\.]+)\.([a-zA-Z0-9\_\-\.]+)$/.test(this) }
function $display(v) { with($(v).style){ if(display=='none') display=''; else display='none'} }