The ISE search system is a temporary hack I wrote as an example of what might be done using eXist, but it's now running live on the site. It's using very old data, but the latest versions of the play files are too complicated to be inserted, so I've written some basic XSLT that strips out all the joinID attributes to simplify them. Running that, and fixing some XML errors in the original files, allows me to insert all but one of the files into the old eXist. The one remaining file is clearly disfunctional, so there's not much I can do with it.
Now the question is how to test this. I've got the new plays in a separate collection from the old ones, and with a modern eXist, I'd just rename the two collections, but the old version doesn't let me do that, so I'd have to delete the old ones and then replace them with the new, leaving the search functionality broken for a period. Waiting for updates from the ISE folks on whether there's a better approach using isebeta.