public Renderer::renderPlain(&$elements)
Renders final HTML in situations where no assets are needed.
Calls ::render() in such a way that placeholders are replaced.
Useful for instance when rendering the values of tokens or emails, which need a render array being turned into a string, but do not need any of the bubbleable metadata (the attached assets and cache tags).
Some of these are a relatively common use case and happen *within* a ::renderRoot() call, but that is generally highly probl