Notice that when you look at, say, the `io` package and are reading the documentation for `func Copy`, that the code supplied for the functional signature links the type declarations. Just follow the links to jump to a given interface to explore.
going to disappoint in saying that you can't read most online documentation cover to cover. i don't know of any that works that way. (unless it's the guide or tutorial part.)
you can use the online documentation as reference though. presumably a book or a guide has already told you about the packages/interfaces/functions/etc. you are looking for.
i have to say that go is one of the best documented language out there. "go doc" should be all one needs if we were all serious about documenting go code/libraries.
https://golang.org/pkg/
Notice that when you look at, say, the `io` package and are reading the documentation for `func Copy`, that the code supplied for the functional signature links the type declarations. Just follow the links to jump to a given interface to explore.