Safecracker validation

Hello Guys , i’m using safecracker form for category entry at control panel , my question how to validate that form so that user must select one of the category provided. thanks before

here is a small piece of my script

{exp:safecracker channel="mobil_baru_listing" return="user_main/mobru_list/{logged_in_member_id}” include_jquery=”no” safecracker_head=”yes” } <select name=”category[]” id=”merek_mobil” > <option value=”“>–Pilih Merek Mobil–</option> {exp:channel:categories channel="mobil_bekas_listing" style="linear" category_group="6" parent_only="yes"} <option value=”{category_id}”>{category_name}</option> {/exp:channel:categories} </select>

{exp:safecracker}