1. A method performed by a data processing apparatus, the method comprising: storing an activity history of a user using a client system, the activity history including at least one of click through rates, conversion rates, and bounce rates associated with presentation styles of content items and publications previously presented to the user on the client system; classifying, by the data processing apparatus, the content items and publications previously presented to the user into categories through analysis of text within the content items and publications that were previously presented; selecting, from among the categories, a category of interest based on the stored activity history that includes the at least one of click through rates, conversion rates, and bounce rates associated with presentation styles of the content items and publications previously presented to the user on the client system; receiving, by the data processing apparatus, a request for supplemental content to be presented with a publication requested by the user of the client system, wherein the supplemental content comprises a body of text having a plurality of terms, and wherein the publication includes one or more slots that reference the supplemental content; determining that one or more terms of the body of text having the plurality of terms comprise a specified type of term or a phrase; identifying that the one or more terms comprising the specified type of term or the phrase are associated with the category of interest selected from among the categories into which the content items and publications, that are previously presented to the user and for which the at least one of click through rates, conversion rates, and bounce rates are stored in the activity history, are classified; identifying a particular presentation style by determining a default presentation style for the determined one or more terms of the body of text having the plurality of terms; selecting the particular presentation style for the determined one or more terms that is different from the default presentation style; modifying the supplemental content referenced by the one or more slots to cause the one or more terms identified as being associated with the selected category of interest to appear in the identified particular presentation style such that the identified one or more terms differ in appearance from other terms of the plurality of terms in the supplemental content; and providing the requested publication with the one or more slots, wherein the one or more slots comprise the modified supplemental content.
1. A method performed by a data processing apparatus, the method comprising: storing an activity history of a user using a client system, the activity history including at least one of click through rates, conversion rates, and bounce rates associated with presentation styles of content items and publications previously presented to the user on the client system; classifying, by the data processing apparatus, the content items and publications previously presented to the user into categories through analysis of text within the content items and publications that were previously presented; selecting, from among the categories, a category of interest based on the stored activity history that includes the at least one of click through rates, conversion rates, and bounce rates associated with presentation styles of the content items and publications previously presented to the user on the client system; receiving, by the data processing apparatus, a request for supplemental content to be presented with a publication requested by the user of the client system, wherein the supplemental content comprises a body of text having a plurality of terms, and wherein the publication includes one or more slots that reference the supplemental content; determining that one or more terms of the body of text having the plurality of terms comprise a specified type of term or a phrase; identifying that the one or more terms comprising the specified type of term or the phrase are associated with the category of interest selected from among the categories into which the content items and publications, that are previously presented to the user and for which the at least one of click through rates, conversion rates, and bounce rates are stored in the activity history, are classified; identifying a particular presentation style by determining a default presentation style for the determined one or more terms of the body of text having the plurality of terms; selecting the particular presentation style for the determined one or more terms that is different from the default presentation style; modifying the supplemental content referenced by the one or more slots to cause the one or more terms identified as being associated with the selected category of interest to appear in the identified particular presentation style such that the identified one or more terms differ in appearance from other terms of the plurality of terms in the supplemental content; and providing the requested publication with the one or more slots, wherein the one or more slots comprise the modified supplemental content. 8. The method of claim 1 , further comprising: identifying one or more additional terms based on a plurality of search terms associated with a plurality of search queries performed by the user previously.