17. The method of claim 11 , wherein each second response portion comprises a callback function that comprises the markup language code, one or more portions of content, one or more resources, or one or more references to resources in the second response portion.
17. The method of claim 11 , wherein each second response portion comprises a callback function that comprises the markup language code, one or more portions of content, one or more resources, or one or more references to resources in the second response portion. 18. The method of claim 17 , wherein: each second response portion further comprises one of a plurality of priority parameter values indicating a relative priority of the second response portion; the page-assembling process executes the callback functions of the second response portions each having a highest priority parameter value before executing callback functions of the second response portions not having the highest priority parameter value; and executing a callback function of a respective second response portion comprises the identifying of the corresponding place-holder node in the model representation the inserting, or causing to be inserted, of the portions of content, resources, or calls to resources in the response portion into the model representation at the location in the model representation determined based on the corresponding matching place-holder node.