A new developer portal version has just been released. It includes the new HTML injection widget, revised code samples, improvements to API reference pages and test console, and more.
If you use the built-in, managed developer portal, your portal will be automatically upgraded within two weeks. Make sure to republish it to upgrade the published portal.
If you self-host the developer portal, you need to merge the source code changes and republish and redeploy your portal manually.
Detailed release notes are available in the developer portal repository.