<script type="text/javascript">
            function CheckForm(objForm)
            {
                var rNums=/[0-9]{1}/;
                if (!rNums.test(objForm.num.value)) 
                {
                        window.alert('请输入一个数字!');
                        objForm.num.focus();
                        return false;
                }
                if (objForm.siteurl.value !='www.dreamdu.com') 
                {
                        window.alert('请输入梦之都的网址!');
                        objForm.siteurl.focus();
                        return false;
                }
                return true;
            }
        </Script>
var rNums=/[0-9]{1}/;这句语法怎么解释，什么作用？谢谢！