go doc is one of my favorite programming tools. You can get information about any function from the command-line, without having to open a browser or manually grep for what you're looking for. How does strings.Index work? "go doc strings.Index"

  func Index(s, substr string) int
      Index returns the index of the first instance of substr in s, or -1 if
      substr is not present in s.

It even tells you what import statement to use to get the version of the code that you're reading the documentation about. It isn't perfect, but it's my favorite documentation tool and would be my number one reason against switching to another language. (For example, I would kill for this in Typescript.)