10. The system of claim 9 , wherein determining the subject matter of the content page comprises performing sentiment analysis or semantic analysis on the online content.
10. The system of claim 9 , wherein determining the subject matter of the content page comprises performing sentiment analysis or semantic analysis on the online content. 11. The system of claim 10 , wherein: determining the subject matter of the content page based on the sentiment analysis comprises determining the subject matter to be a positive sentiment; and the instructions cause the one or more data processing apparatus to perform operations comprising selecting the comment based on the positive sentiment.