rel attribute for performance and security

The rel attribute on HTML links need to be set to noopener if you're using target=_blank in your links, otherwise the new tab contains a reference to the other tab's window object, and can redirect, manipulate dom, etc.

Read more and see a demo here: https://mathiasbynens.github.io/rel-noopener

There are also some performance benefits: https://jakearchibald.com/2016/performance-benefits-of-rel-noopener/