code: func FindIndex(in []byte, pos, index int) ([]byte, error) {
  	pos, err := skipSpace(in, pos)
  	if err != nil {
  		return nil, err
  	}
  
  	if v := in[pos]; v != '[' {
  		return nil, newError(pos, v)
  	}
  	pos++
  
  	idx := 0
  	for {
  		pos, err = skipSpace(in, pos)
  		if err != nil {
  			return nil, err
  		}
  
  		itemStart := pos
  		// data
  		pos, err = Any(in, pos)
  		if err != nil {
  			return nil, err
  		}
  		if index == idx {
  			return in[itemStart:pos], nil
  		}
  
  		pos, err = skipSpace(in, pos)
  		if err != nil {
  			return nil, err
  		}
  
  		switch in[pos] {
  		case ',':
  			pos++
  		case ']':
  			return nil, errIndexOutOfBounds
  		}
  
  		idx++
  	}
  }
docs: // FindIndex accepts a JSON array and return the value of the element at the specified index