US Patent 9083600 Providing presence information within digital items

Providing presence information within digital items is described. In one example, a server system receives presence information from a plurality of client devices. The presence information indicates a portion of a digital item associated with at least one user of each respective client device. The server system also receives a user identification request from a requesting client device to identify one or more users of the plurality of client devices associated with a particular portion of the digital item. Additionally, the server system identifies a user of a particular client device associated with the particular portion of the digital item based on the presence information of the particular client device and sends an identifier of the user of the particular client device to the requesting client device.