Explanation/Reference:
* The val() method returns or sets the value attribute of the selected elements.
* HTML <input> pattern Attribute
The pattern attribute specifies a regular expression that the <input> element's value is checked against.
Example
An HTML form with an input field that can contain only three letters (no numbers or special characters):
<form action="demo_form.asp">
Country code: <input type="text" name="country_code"
pattern="[A-Za-z]{3}" title="Three letter country code">
<input type="submit">
</form>
Reference: HTML <input> pattern Attribute
http://www.w3schools.com/tags/att_input_pattern.asp