How wherePivot() actually works internally in laravel 5?

How wherePivot() actually works internally in laravel 5 ?

For Example I was practicing by watching a tutorial and the teacher was using wherePivot() for construing relationship:

public function friendsOfMine(){

    return $this->belongsToMany('Chatty\Models\User','friends','user_id','friend_id');
}

public function friendOf(){

  return $this->belongsToMany('Chatty\Models\User','friends','friend_id','user_id');

}

public function friends(){

  return $this->friendsOfMine()->wherePivot('accepted',true)->get()->merge($this->friendOf()->wherePivot('accepted',true)->get());

} 

via Chebli Mohamed