# File lib/state_machine/node_collection.rb, line 19
    def initialize(machine, options = {})
      assert_valid_keys(options, :index)
      options = {:index => :name}.merge(options)
      
      @machine = machine
      @nodes = []
      @indices = Array(options[:index]).inject({}) {|indices, attribute| indices[attribute] = {}; indices}
      @default_index = Array(options[:index]).first
    end