$re = '/\b(?<=class=\")[^"]+(?=\")/m';
$str = '<div class="hero-slider_control-wrap bot-element">
<div class="hero-slider_control hero-slider-button-next">
<span>
Next
<i class="fal fa-angle-right"></i>
</span>
</div>
<div class="hero-slider_control hero-slider-button-prev">
<span>
<i class="fal fa-angle-left"></i>
Prev
</span>
</div>
</div>';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php