Not sure if this will work across apache versions? Tested on Apache 2.2
Prevents preview files from being cached in the browser and that always the newest version will be served. Otherwise the user will need to use ctrl+r or something to reload a page that includes a preview file to make sure the cache is ignored and many users would not know that.
Tested locally, it works on apache 2.4, however I had one problem. If mod_headers isn't enabled, apache will just issue 500 errors (for everything in the folder, not just preview JS files).
can you check if that works?