//Declare variables
var defaultEmptyOK = true;
var reEmail = /^.+\@.+\..+$/ //regular expression

// Email address must be of form a@b.c
function isEmail (s) {  
	if (isEmpty(s)) {
		return false;
	}
	return reEmail.test(s)
}

function isEmailList(s) {
	var addresses = s.split(",");
	for (var i = 0; i < addresses.length; i++) {
		if (!isEmail(addresses[i].replace(/^\s+|\s+$/g,""))) {
			return false;
		}
	}
	return addresses.length > 0;
}

// Check whether string s is empty.
function isEmpty(s) {   
	return ((s == null) || (s.length == 0))
}

function checkEnter(e){ //e is event object passed from function invocation
	var characterCode; // literal character code will be stored in this variable
	if(e && e.which) { //if which property of event object is supported (NN4)
		e = e
		characterCode = e.which //character code is contained in NN4's which property
	}
	else{
		e = event
		characterCode = e.keyCode //character code is contained in IE's keyCode property
	}
	if(characterCode == 13){ //if generated character code is equal to ascii 13 (if enter key)
		return false
	}
	else{
		return true
	}
}