instance method set_enablement

# File activemodel/lib/active_model/observer_array.rb, line 119
      def set_enablement(enabled, observers)
        if block_given?
          transaction do
            set_enablement(enabled, observers)
            yield
          end
        else
          observers = ActiveModel::Observer.descendants if observers == [:all]
          observers.each do |obs|
            klass = observer_class_for(obs)

            unless klass < ActiveModel::Observer
              raise ArgumentError.new("#{obs} does not refer to a valid observer")
            end

            if enabled
              disabled_observers.delete(klass)
            else
              disabled_observers << klass
            end
          end

          each_subclass_array do |array|
            array.set_enablement(enabled, observers)
          end
        end
      end