This afternoon, I spent some time experimenting with opmlPackage from Dave Winer, focusing on the new feature to include other OPML files within an OPML file. The includes feature is only part of the Node version of the package (other features can be used in a browser). I changed the OPML file that had example includes to use three reading list files that I had in OPML format. I then changed the demo script to add logic to write out the new outline as a file (you can see it in this Gist) and ran it locally on my laptop. Finally, I created another copy of the OPML client to display the new outline (you can see it here). Looks like the includes feature is working fine!