使用Golang中的结构体将方法转换为函数

I read some strange codes which convert a method to a function whose first argument is a pointer to this method's struct.

I write an example to demonstrate it:

package main

import "fmt"

type fooS struct{}

func (s *fooS) fooF(fooArg interface{}) {
    fmt.Println("fooF: ", fooArg)
}

type wowS struct {
    callback func(s *fooS, fooArg interface{})
}

func main() {
    wow := new(wowS)
    wow.callback = (*fooS).fooF // strange
    wow.callback(nil, 123)
}

The example's syntax is strange but has no error.

Can any one tell me how these codes work or give me an official document about them?

Thanks:)