does_not_support_reverse?

# File activerecord/lib/active_record/relation/query_methods.rb, line 1143
    def does_not_support_reverse?(order)
      #uses sql function with multiple arguments
      order =~ /\([^()]*,[^()]*\)/ ||
        # uses "nulls first" like construction
        order =~ /nulls (first|last)\Z/
    end