1. A method, comprising: receiving, at a content server via a first network connection, a request for content from a client device, where the content comprises a plurality of portions represented within a root document; determining to defer at least one portion of the content for download via a network connection other than the first network connection based upon a download constraint of the at least one portion of the content and a network characteristic of the first network connection; and sending the content with each of the at least one portion of the content replaced with a content stub within the root document, where each content stub identifies the respective portion of the content as a deferred portion of the content and comprises a content identifier of the respective deferred portion of the content.