    # File lib/active_support/callbacks.rb, line 99
          def |(chain)
            if chain.is_a?(CallbackChain)
              chain.each { |callback| self | callback }
            else
              if (found_callback = find(chain)) && (index = index(chain))
                self[index] = chain
              else
                self << chain
              end
            end
            self
          end