# File lib/rspec/core/example_group.rb, line 180
      def self.describe(*args, &example_group_block)
        @_subclass_count ||= 0
        @_subclass_count += 1
        args << {} unless args.last.is_a?(Hash)
        args.last.update(:example_group_block => example_group_block)

        # TODO 2010-05-05: Because we don't know if const_set is thread-safe
        child = const_set(
          "Nested_#{@_subclass_count}",
          subclass(self, args, &example_group_block)
        )
        children << child
        child
      end