mixed preg_filter ( mixed $pattern , mixed $replacement , mixed $subject [, int $limit = -1 [, int &$count ]] )
preg_filter() is identical to preg_replace() except it only returns the (possibly transformed) subjects where there was a match. For details about how this function works, read the preg_replace() documentation.
Returns an array if the subject parameter is an array, or a string otherwise. If no matches are found or an error occurred, an empty array is returned when subject is an array or NULL otherwise.