brew/Library/Homebrew/cask/lib/hbc/container/pkg.rb

require "hbc/container/naked"

module Hbc
  class Container
    class Pkg < Naked
      def self.me?(criteria)
        criteria.extension(/m?pkg$/) &&
          (criteria.path.directory? ||
           criteria.magic_number(/^xar!/n))
      end
    end
  end
end