What does adding vidstack as a vite bundler plugin do?

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What does adding vidstack as a vite bundler plugin do?

The SvelteKit Installation Guide says to set up the bundler by adding vidstack as a plugin like this:

import { sveltekit } from '@sveltejs/kit/vite';
import { vite as vidstack } from 'vidstack/plugins';
import { defineConfig } from 'vite';

export default defineConfig({
  plugins: [vidstack(), sveltekit()],
});

However, the Svelte example sets up the bundler without adding vidstack as a plugin:

import { svelte } from '@sveltejs/vite-plugin-svelte';
import { defineConfig } from 'vite';

// https://vitejs.dev/config
export default defineConfig({
  plugins: [svelte()],
});