only WebKit and Firefox Nightly builds have implemented [it]
[...] There is also an intent to ship in Blink too.
(Opera is based on Chromium that uses the WebKit fork "Blink")
Offtopic: first time in years, I see the opera.com website. There was a lot of useful information in their blog posts, when they still worked on their own browser engine.
Offtopic: first time in years, I see the opera.com website. There was a lot of useful information in their blog posts, when they still worked on their own browser engine.