This test will check if all links to external pages that have the target='_blank' attribute also have the rel='noopener' or rel='noreferrer' attribute. When you link to an external site using the target='_blank' attribute, security and performance issues arise: The external pages you link to may run on the same process as your page. If the other page is running a lot of JavaScript, your page's performance may suffer. The other page can access your window object with the window.opener property. This may allow the other page to redirect your page to a malicious URL. Adding rel='noopener' or rel='noreferrer' to your target='_blank' links avoids these issues.