code: func (v *View) mergeLines(y int) error {
  	v.tainted = true
  
  	_, y, err := v.realPosition(0, y)
  	if err != nil {
  		return err
  	}
  
  	if y < 0 || y >= len(v.lines) {
  		return errors.New("invalid point")
  	}
  
  	if y < len(v.lines)-1 { // otherwise we don't need to merge anything
  		v.lines[y] = append(v.lines[y], v.lines[y+1]...)
  		v.lines = append(v.lines[:y+1], v.lines[y+2:]...)
  	}
  	return nil
  }
docs: // mergeLines merges the lines "y" and "y+1" if possible.