11. The system of claim 9 , wherein the operations further comprise: estimating performance metrics for a plurality of candidate advertisements; and identifying a candidate advertisement from the plurality of candidate advertisements with performance metrics greater than a performance threshold.
11. The system of claim 9 , wherein the operations further comprise: estimating performance metrics for a plurality of candidate advertisements; and identifying a candidate advertisement from the plurality of candidate advertisements with performance metrics greater than a performance threshold. 12. The system of claim 11 , wherein the instructions comprise: identifying a plurality of candidate advertisements based on a context of the document or advertisements related to the selected advertisements.