4. The one or more computer-readable media as recited in claim 1 , wherein at least one text portion of the at least the third text portion and the fourth text portion of the third electronic book is a highest-ranked text portion of the at least the third text portion and the fourth text portion of the third electronic book, the operations further comprising: including an indication of the highest-ranked text portion in metadata associated with the third electronic book; and sending the metadata to a user device to identify the highest-ranked text portion of the third electronic book.
1. One or more computer-readable media maintaining instructions, which when executed by one or more processors, cause the one or more processors to perform operations comprising: accessing training data, the training data comprising: a first text portion from a first electronic book, the first text portion associated with a positive feedback through a first user interaction received by a first computing device associated with a first user, and a second text portion from a second electronic book, the second text portion associated with a negative feedback through a second user interaction received by a second computing device associated with a second user; training a classifier based at least in part on the training data; applying the classifier to a text of a third electronic book, wherein the classifier: assigns, to a third text portion of the text of the third electronic book and independent of annotation data associated with the third electronic book, a first score that indicates a probability that the third text portion will be annotated by future users, assigns, to a fourth text portion of the text of the third electronic book and independent of annotation data associated with the third electronic book, a second score indicating a probability that the fourth text portion will be annotated by future users, wherein the first score and the second score are assigned based at least in part on the positive feedback received through the first user interaction, the negative feedback received through the second user interaction, and at least one of: a similarity to a sentence structure of the at least one of the first text portion or the second text portion, or a similarity to at least one of a type of words used in the first text portion or a type of words used in the second text portion; and determines a ranking of at least the third text portion and the fourth text portion of the third electronic book based at least in part on the first score and the second score; and selecting at least one of the third text portion or the fourth text portion based at least in part on the ranking.