$re = '/<(b|i)>(.*?)(<br>)+(.*?)<\/\1>/';
$str = '<b> текст <i>вложение <br> </i> переход</b><b> текст <i>вложение <br> </i> переход</b><b> текст <i>вложение <br> </i> переход</b>';
$subst = "<$1>$2</$1>$3<$1>$4</$1>";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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