relnoopener

Relnoopener refers to the rel="noopener" attribute value used on links that are opened in a new browsing context with target="_blank". It is a web security feature designed to prevent the opened page from gaining access to the window object of the page that opened it.

Without noopener, the new page can access window.opener and potentially manipulate the original page, a class of attack commonly called tabnabbing or phishing. By setting noopener, the browser ensures that the opened page's window.opener is null, preventing scripts on the new page from controlling or redirecting the originating page.

In practice, developers typically apply rel="noopener" to external links that open in a new tab or window. For broader privacy or compatibility, rel="noreferrer" can be used to also suppress the Referer header sent to the destination. The common pattern rel="noopener noreferrer" covers both protections, and many developers use it as a default for external links. Some browsers treat "noreferrer" as implying "noopener," but behavior can vary across environments, so explicit usage of "noopener" is generally recommended.

Compatibility and usage: relnoopener is supported by all major modern browsers (Chrome, Firefox, Edge, Safari). It is considered a best practice when using target="_blank" to reduce the risk of tabnabbing and other opener-based attacks. While it does not replace other security measures, it provides a simple, effective defense for external links opened in new contexts.