$re = '/<(a|p|b)>.*?<\/\1>/';
$str = '<b>Ключ <br> 1:</b>Значение 1<br><b>Ключ 2:</b>Значение 2<br><b>Ключ 3:</b>Значение 3<br><b>Ключ 4:</b>Знач ение 4<br>
<b>Ключ <br> 1:</b>Значение 1<br>
<b>Ключ 2:</b>Значение 2<br>
<b>Ключ 3:</b>Значение 3<br>
<b>Ключ 4:</b>Значение 4<br>';
preg_match_all($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