rescue_from (ActiveSupport::Rescuable::ClassMethods)

    # File lib/active_support/rescuable.rb, line 44
          def rescue_from(*klasses, &block)
            options = klasses.extract_options!

            unless options.has_key?(:with)
              if block_given?
                options[:with] = block
              else
                raise ArgumentError, "Need a handler. Supply an options hash that has a :with key as the last argument."
              end
            end

            klasses.each do |klass|
              key = if klass.is_a?(Class) && klass <= Exception
                klass.name
              elsif klass.is_a?(String)
                klass
              else
                raise ArgumentError, "#{klass} is neither an Exception nor a String"
              end

              # put the new handler at the end because the list is read in reverse
              rescue_handlers << [key, options[:with]]
            end
          end