Online PHP editor | refs for SjRfI

<?php $headers = <<<HEADERS # Hello ## World ### Let's add ## Some headers ### Yay! # Foo ## Bar ## Bar Again HEADERS; $levels = []; echo preg_replace_callback( '~^(#+)\K~m', function($m) use (&$levels) { $hashes = strlen($m[1]); $index = $hashes - 1; $reduction = sizeof($levels) - $hashes; if (!isset($levels[$index])) { $levels[$index] = 1; } else { ++$levels[$index]; } if ($reduction > 0) { $levels = array_slice($levels, 0, -$reduction); } return " " . implode('.', $levels); }, $headers );