def +(other)
      case other
      when Offset
        Offset.new(self.line + other.line, self.column + other.column)
      when Integer
        Offset.new(self.line + other, self.column)
      else
        raise ArgumentError, "can't convert #{other} into #{self.class}"
      end
    end
def +(other)
      case other
      when Offset
        Offset.new(self.line + other.line, self.column + other.column)
      when Integer
        Offset.new(self.line + other, self.column)
      else
        raise ArgumentError, "can't convert #{other} into #{self.class}"
      end
    end
Public: Shift the offset by some value.

 other - An Offset to add by its line and column
         Or an Integer to add by line

 Returns a new Offset instance.