lorem
description 1
lorem
description 2
lorem
description 3
lorem
description 4
lorem
description 5
lorem
description 6";
$i = 1;
$matches = null;
while (true) {
$text = preg_replace('|<(/)?b>|', ('<\1h'.$i.'>'), $text, 2, $matches);
if (!$matches) {
break;
}
if ($i < 4) $i++;
$matches = null;
}
echo $text;