<?php if ( '~(?(DEFINE)(?<content>\w+))(?><(?&content)>|\[(?&content)\]|\((?&content)\))~', '<123> [234] (45) 6 (<78>)', $m ) ) ?>
Standard input is empty
Array ( [0] => Array ( [0] => <123> [1] => [234] [2] => (45) [3] => <78> ) [content] => Array ( [0] => [1] => [2] => [3] => ) [1] => Array ( [0] => [1] => [2] => [3] => ) )