如何获取字符串中嵌套标签的完整内容？

$str = "{if 'a'}    111111    {if 'c'}33333{/if}    {if 'd'}44444{/if}    ......{/if}{if 'b'}22222{/if}";

["{if 'a'}    111111    {if 'c'}33333{/if}    {if 'd'}44444{/if}    ......{/if}","{if 'b'}22222{/if}"]

$stack = [];$top = null;$result = [];preg_match_all('!({/?if)!', $str, $matches, PREG_OFFSET_CAPTURE);foreach ($matches[0] as [$match, $offset]) {    if ($match === '{if') {        $stack[] = $offset;        if ($top === null) { $top = $offset; }    } else {        $pop = array_pop($stack);        if ($pop === null) { throw new Exception('语法错误，存在多余的 {/if} 标签'); }        if (empty($stack)) {            $newOffset = $offset + strlen($match);            $result[] = substr($str, $top, $newOffset);            $top = $newOffset + 1;        }    }}if (!empty($stack)) { throw new Exception('语法错误，存在未闭合的 {if} 标签'); }var_dump($result);