http.Dir的文档在哪里

I'm trying to set up a go file server and came across the function http.Dir(path string) http.FileSystem when I looked into the documentation for FileSystem.

In the source of net/http/fs.go line 705 it says:

//To use the operating system's file system implementation,
//
// use http.Dir:
//
//     http.Handle("/", http.FileServer(http.Dir("/tmp")))

But I can't find any Documentation of this function. Am I missing something?

Edit: I missed that it's a type