<link href="//maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<div class="container">
<h1 class="text-center mt-2 mb-3"><a href="http://bootstraptema.ru/stuff/snippets_bootstrap/form/html5_form_validation_bootstrap/30-1-0-2724" target="_blank">HTML5 Form Validation Bootstrap with pattern matching, with custom inline error message</a></h1>
<form>
<div class="form-row">
<div class="col">
<input type="text" class="form-control" pattern="[а-яА-Яa-zA-Z0-9_-]{4,12}" autofocus required title="Введите от 4 до 12 символов" placeholder="RU/EN sumbols">
</div>
<div class="col">
<input type="submit" class="btn btn-primary" value="Проверить">
</div>
</div>
</form>
</div>
