Omitting params in rake task call
===

Lets say I have a rake task

    task :aa, [:pp1, :pp2, :pp3] do |t, args|
      args.with_defaults(:pp2 => "fff")
      puts args.pp1
      puts args.pp2
      puts args.pp3
    end

How do I pass to rake only 1st and 3rd param, taking the second one from defaults? Object of what type is a thing in square brackets in "rake aa[1,2,3]" call?