What does whitelist and blacklist do in Browser-sync?

Question

I am trying to figure out what the following code means.

gulp.task('browsersync', function() {
  browserSync.init({
    proxy: browsersync_proxy,
    notify: false,
    open: false,
    snippetOptions: {
      whitelist: ['/wp-admin/admin-ajax.php'],
      blacklist: []
    }
  });
});

I look at the documentation but there is not much descriptions about snippetOptions. Can you help to give me more explanations on whitelist and blacklist here?