def keyword(text = nil, match = nil, &block)
      biddable_criterion = BiddableAdGroupCriterion.new(self)
      criterion = CriterionKeyword.new(self, text, match, &block)
      biddable_criterion.criterion = criterion
      @criterions ||= []
      @criterions.push( biddable_criterion )
      biddable_criterion
    end
def keyword(text = nil, match = nil, &block)
      biddable_criterion = BiddableAdGroupCriterion.new(self)
      criterion = CriterionKeyword.new(self, text, match, &block)
      biddable_criterion.criterion = criterion
      @criterions ||= []
      @criterions.push( biddable_criterion )
      biddable_criterion
    end
instantiate an BiddableAdGroupCriterion but it is called 'keyword' for convenience

 http://code.google.com/apis/adwords/v2009/docs/reference/AdGroupCriterionService.BiddableAdGroupCriterion.html