As I've gotten to learn many different languages (PHP, Ruby, Go, Java, Python, etc) over the last 10 years, it has been really interesting to see how different languages and communities can vary so wildly in their quality of documentation.
As it relates to programming languages, Go's "Tour of Go" (https://tour.golang.org/welcome/1) is an excellent introduction to the language. I wish every language had an intro guide as good.
In terms of frameworks, I absolutely love the Ruby on Rails guides. They strike the right balance between staying high level enough for me to build a mental model of how the framework is working under the hood, while getting deep enough to be useful to solve individual problems I have.
Overall, I think the Ruby community has done a great job of documenting their libraries and frameworks. Whether it's Rails or Sinatra, or it's a library like Devise, Ruby OSS projects seem to tend towards thorough documentation.
On the flip side, Spring's documentation (and most Java library documentation) is absolutely atrocious. Spring in particular only seems to give you 2 flavors of documentation: a 10-minute tutorial, or a 1000-page deep dive in all of the corners of the framework. And Java libraries in general seem to have miserable, out-of-date, incomplete documentation.