methods - レシーバー自体を返すメソッド (Go) の目的は何ですか?

Question

pkg go/token のこの関数は、レシーバ自体を返すメソッドが必要な理由を不思議に思います。

// Token source positions are represented by a Position value.
// A Position is valid if the line number is > 0.
//
type Position struct {
    Filename string; // filename, if any
    Offset   int;    // byte offset, starting at 0
    Line     int;    // line number, starting at 1
    Column   int;    // column number, starting at 1 (character count)
}


// Pos is an accessor method for anonymous Position fields.
// It returns its receiver.
//
func (pos *Position) Pos() Position { return *pos }