code: func (ui *UIHandler) serveFromDiskOrStatic(rw http.ResponseWriter, req *http.Request, rx *regexp.Regexp, disk http.Handler, static *fileembed.Files) {
  	suffix := httputil.PathSuffix(req)
  	m := rx.FindStringSubmatch(suffix)
  	if m == nil {
  		panic("Caller should verify that rx matches")
  	}
  	file := m[1]
  	if disk != nil {
  		req.URL.Path = "/" + file
  		disk.ServeHTTP(rw, req)
  	} else {
  		ServeStaticFile(rw, req, static, file)
  	}
  
  }
docs: // serveFromDiskOrStatic matches rx against req's path and serves the match either from disk (if non-nil) or from static (embedded in the binary).