Hello Sam, this is currently done in the build-site command (
in the build_site script) via phantomjs. This is a much deprecated way (should be substituted with Puppeteer or Playwright), but it works. An ideal solution would be to refactor the core so that the core .js files are importable and use just the 
generateRSS method, but it requires to also refactor building core, which probably requires more time and considerations that I currently have, so as a quick solution, I can suggest reusing the bits from the build_site script.