The Observable docs mention ECMAScript Observable, which I’m pretty sure is dead. You might want to delete that sentence.
I was not aware of the fact that it is dead 
It hasn’t been updated in 6 years or so, but RXJS is still one of the implementation of this spec ( Observable (tc39.es)). I don’t mind if anyone removes this comment though, as it doesn’t influence the content of the page. Pages can be edited on github