I have downloaded a starter for form controls for mysql user registration page. Everything seems to work fine with bootstrap 3 (not 4) in terms of styling when error. I took a closer look at the code and am scratching my head about something, below is a snippet of the form:
<div class="form-group <?php echo (!empty($city_err)) ? 'has-error' : ''; ?>">
<label>City</label>
<input type="text" name="city" class="form-control" value="<?php echo $city; ?>">
<span class="help-block"><?php echo $city_err; ?></span>
</div>
If you look at the class, the error message is in the quotation marks (for class). I'm assuming this is a typo, because I don't know why that would be a class, but then what's going on with the error message? It has to be assigned an HTML tag, but which one?