function isEmailAddress(string) {
    return /^[^@]+@[^.]+(\.[^.]+)+$/.test(string);
}

function validate(form) {
    var controls = form.elements,
        transaction = controls['transaction'].value;
        cargo = controls['cargo'].value;

    if (transaction != 0 && cargo != 0) {
        alert('Please enter a Cargo number # or a Trasaction number # but not both');
        return false;
    }

    /* More validation */

    return true;
}