1. A computer-implemented method of providing information about named entities referenced in content of an electronic book (“ebook”), comprising: receiving, from a client device, an ebook identifier identifying the ebook; determining, using the ebook identifier, a set of layers available for use with the ebook, the layers in the set providing information associated with the ebook, different layers in the set providing different types of information, and a layer in the set providing information associated with named entities referenced in content of the ebook; receiving, from the client device, a content range identifying a range of content of the ebook for which layer information is requested and an identification of one or more of the layers in the set for which layer information is requested; and transmitting, to the client device, layer information associated with the ebook content identified by the content range for the identified layers, the transmitted layer information including information associated with named entities referenced by ebook content in the content range.