class SourceMap::Offset

def +(other)

Returns a new Offset instance.

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

Public: Shift the offset by some value. 
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