# File lib/logging.rb, line 347
    def backtrace( b = nil )
      @backtrace = true unless defined? @backtrace
      return @backtrace if b.nil?

      @backtrace = case b
          when :on, 'on', true;    true
          when :off, 'off', false; false
          else
            raise ArgumentError, "backtrace must be true or false"
          end
    end