Use custom regular expressions to validate form
<form id="loginForm" name="loginForm">
                    <ul>
                        <li>
                            <label for="Username">Username:</label>
                            <input type="email" data-validation-error="Please enter a username" data-validation-use="^([a-zA-Z0-9_-.]+)@(([[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.)|(([a-zA-Z0-9-]+.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(]?)$" id="username" name="username" maxlength="254" class="required" />
                        </li>
                        <li>
                            <label for="Password">Password:</label>
                            <input type="password" data-validation-error="Please enter a password" data-validation-use="^[a-zA-Z]w{5,12}$" id="password" name="password" value="" maxlength="12" class="required" />
                        </li>
                    </ul>
                    <input type="submit" value="Login" class="button" name="loginBtn" id="loginBtn" />
            </form>

<input type="email" required />

$('form').submit(function(){
    var isValid = true;
    $(this).find(':input').each(function(){
        var regex = new RegExp($(this).attr('data-validation-use'));
        if(!regex.exec($(this).val())){
            $('.validationError').append($(this).attr('data-validation-error'));
            $(this).addClass('invalid');
            isValid = false;
        }
    });
    return isValid;
});