1. Apparatus for assembling content fragments into a container, wherein the container comprises markup identifying one or more content fragments, comprising: a hardware processor; computer memory that includes a first queue, and a second queue; the computer memory holding computer program instructions that when executed by the hardware processor perform the following method: receiving, by a host process, a request for the container, and placing the request in the second queue; removing from the second queue, by a first execution thread, the request, and processing the request to generate a data object; instantiating a software processor; generating, by the software processor, a parse tree representation of the container, the parse tree representation including an edge side include (ESI) code directive associated with at least one content fragment in the container; cloning the parse tree representation in a cache; processing, by the software processor, and from top to bottom of the parse tree representation, each ESI code directive, wherein, if an ESI code directive in the parse tree representation is an ESI include, placing a request associated with the ESI include in the first queue for handling by a second execution thread; as ESI code directives are processed, having the software processor concatenate results into the data object; after the parse tree representation is parsed from top to bottom, placing the data object on the first queue; retrieving, by the second execution thread, the data object, and building a response to the request for the container; and serving the response.
7. The apparatus as described in claim 1 wherein the ESI code directive is a conditional include.