code: func (l *List) AddAt(pos uint, entries ...interface{}) {
  	l.key.Lock()
  	defer l.key.Unlock()
  
  	l.underlyer = append(l.underlyer[:pos], append(entries, l.underlyer[pos:]...)...)
  }
docs: // AddAt injects values beginning at `pos`. If multiple values
  // are provided in `entries` they are placed in the same order
  // they are provided.