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<html><body>function countLetters($matches) { return $matches[0] . '[' . strlen($matches[0]) . 'letter]';}function countDigits($matches) { return $matches[0] . '[' . strlen($matches[0]) . 'digit]';}$input = "365 days";$patterns = [ '/[a-z]+/i' => 'countLetters', '/[0-9]+/' => 'countDigits'];$result = preg_replace_callback_array($patterns, $input);echo $result;</body></html>
365[3digit] days[4[1digit]letter]