# File lib/sass/tree/visitors/to_css.rb, line 111
  def prepend!(prefix)
    @result.insert 0, prefix
    return unless @source_mapping

    line_delta = prefix.count("\n")
    offset_delta = prefix.gsub(/.*\n/, '').size
    @source_mapping.shift_output_offsets(offset_delta)
    @source_mapping.shift_output_lines(line_delta)
  end