Show pagesourceBacklinksCite current pageExport to PDFBack to top Share via Share via... Twitter LinkedIn Facebook Pinterest Telegram WhatsApp Yammer Reddit TeamsRecent ChangesSend via e-MailPrintPermalink × Confirming that a product or service meets the needs of its users. External validation Internal validation. validation.txt Last modified: 2022/01/05 11:37by 127.0.0.1