# File lib/asciidoctor/extensions.rb, line 532
    def activate document
      @document = document
      (Extensions.groups.values + @groups.values).each do |group|
        case group
        when ::Proc
          case group.arity
          when 0, -1
            instance_exec(&group)
          when 1
            group.call self
          end
        when ::Class
          group.new.activate self
        else
          group.activate self
        end
      end
      self
    end