$("#myForm").validate({
    rules: {
        name: {
            required: true,
            lettersOnly: true
        },
        email: {
            required: true,
            email: true
        },
        phone: {
            required: true,
            digits: true,
            minlength: 9,
            maxlength: 9
        },
        birthday: {
            required: true,
            dateISO: true
        }
    },
    messages: {
        name: {
            required: "Please enter your name",
            lettersOnly: "Please enter only letters and spaces"
        },
        email: {
            required: "Please enter your email",
            email: "Please enter a valid email address"
        },
        phone: {
            required: "Please enter your phone",
            digits: "Please enter only numbers",
            minlength: "Please enter 9 digits only",
            maxlength: "Please enter 9 digits only"
        },
        birthday: {
            required: "Please enter your birthday",
            dateISO: "Please enter a valid date"
        },
    },
    submitHandler: function(form) {
        form.submit();
    }
});

jQuery.validator.addMethod("lettersOnly", function(value, element) {
    return value.match(new RegExp("^[a-zA-Z ]+$"));
});