1. A computer-implemented method comprising: receiving, at a first computer system and from a client computing device, a request for a first electronic document that is hosted by a second computer system that is separate from the first computer system; obtaining, by the first computer system and from the second computer system, the first electronic document; determining, at the first computer system, whether or not to process the first electronic document based on an identity of the second computer system; when the first computer system determines to not process the first electronic document: providing the first electronic document, by the first computer system and to the client computing device, as a response to the request from the client computing device for the first electronic document; and when the first computer system determines to process the first electronic document: identifying one or more portions of the first electronic document that a device of a device type that corresponds to the client computing device is not configured to interpret or execute, the one or more portions comprising interpreted language elements, converting the one or more portions of the first electronic document, by the first computer system and in response to the identifying, into one or more portions of replacement content that are of one or more content types that a device of a device type that corresponds to the client computing device is configured to interpret or execute, generating a second electronic document that includes i) the one or more portions of replacement content and ii) other portions from the first electronic document that a device of a device type that corresponds to the client computing device is configured to interpret or execute, and providing the second electronic document, by the first computer system and to the client computing device, as a response to the request from the client computing device for the first electronic document.