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/**
* WooCommerce: Marcar los productos agotados
*/

add_action( 'woocommerce_before_shop_loop_item_title', 'mg_display_sold_out_loop_woocommerce' );
 
function mg_display_sold_out_loop_woocommerce() {
    global $product;
 
    if ( !$product->is_in_stock() && !is_product() ) {
        echo '<span class="agotado">' . __( 'AGOTADO', 'woocommerce' ) . '</span>';
    }
}