1. A client system, comprising: a processor; and a memory containing a program that, when executed on the processor, performs an operation, comprising: receiving, over a data communication network, an electronic document comprising a request to retrieve a plurality of advertisement creatives, wherein the request specifies an advertisement management system and a single identification tag identifying a plurality of advertisement types to be inserted within the electronic document, wherein the plurality of advertisement types comprises all advertisement types to appear within the electronic document, and wherein each of the plurality of advertisement creatives comprises computer program code configured to request a respective advertisement of a type selected from one of the plurality of advertisement types; responsive to transmitting the request specified within the received electronic document to the advertisement management system, receiving, over the data communication network from the advertisement management system, a single software object, wherein the advertisement management system is configured to select the plurality of advertisement creatives based on the plurality of advertisement types identified by the single identification tag specified within the transmitted request, and wherein the single software object comprises a JavaScript object notation (JSON) object that defines all of the plurality of advertisement creatives and identifies how the advertisement creatives will be displayed by the browser: extracting, without requiring user interaction, all of the plurality of advertisement creatives from the single software object by referencing a library configured to interpret the single software object; inserting, without requiring user interaction, each of the plurality of advertisement creatives into the electronic document, prior to rendering the electronic document; and rendering the electronic document together with the plurality of advertisement creatives.
1. A client system, comprising: a processor; and a memory containing a program that, when executed on the processor, performs an operation, comprising: receiving, over a data communication network, an electronic document comprising a request to retrieve a plurality of advertisement creatives, wherein the request specifies an advertisement management system and a single identification tag identifying a plurality of advertisement types to be inserted within the electronic document, wherein the plurality of advertisement types comprises all advertisement types to appear within the electronic document, and wherein each of the plurality of advertisement creatives comprises computer program code configured to request a respective advertisement of a type selected from one of the plurality of advertisement types; responsive to transmitting the request specified within the received electronic document to the advertisement management system, receiving, over the data communication network from the advertisement management system, a single software object, wherein the advertisement management system is configured to select the plurality of advertisement creatives based on the plurality of advertisement types identified by the single identification tag specified within the transmitted request, and wherein the single software object comprises a JavaScript object notation (JSON) object that defines all of the plurality of advertisement creatives and identifies how the advertisement creatives will be displayed by the browser: extracting, without requiring user interaction, all of the plurality of advertisement creatives from the single software object by referencing a library configured to interpret the single software object; inserting, without requiring user interaction, each of the plurality of advertisement creatives into the electronic document, prior to rendering the electronic document; and rendering the electronic document together with the plurality of advertisement creatives. 2. The system of claim 1 , wherein the electronic document comprises a web page that is received from a web server, and wherein the web server is distinct from the advertisement management system.