приложение-оболочка
App shell is a way to render a portion of your application using a route at build time.
This gives users a meaningful first paint of your application that appears quickly because the browser can render static HTML and CSS without the need to initialize JavaScript.
You can use the Angular CLI to generate an app shell.
This can improve the user experience by quickly launching a static rendered page while the browser downloads the full client version and switches to it automatically after the code loads.
A static rendered page is a skeleton common to all pages
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