'[product_id_prefix symbol="0" max-size=11]', ); public $display_name = 'Product id prefix'; public function getValue($post, $field) { $prefixSymbol = isset($field['args']['symbol']) ? $field['args']['symbol'] : '0'; $maxSize = isset($field['args']['max-size']) ? $field['args']['max-size'] : 0; return str_pad($post->ID, $maxSize, $prefixSymbol, STR_PAD_LEFT); } }