How to create a composite process with drill-down to another data flow model.

I am at a loss about how to create a composite process that I can use to "drill down" to other data flow diagrams. The documentation states .."A composite process consists of multiple outer processes. The data flow model allows you to drill down to child processes through a composite process. This means that a top-level process can drill down to another full data flow model."

I cannot find anything in the documentation or online on how to accomplish this. Any assistance would be greatly appreciated!