Instruction: Discuss the purposes and differences between Custom App and Custom Document in a Next.js application.
Context: This question is designed to evaluate the candidate's knowledge of extending the default structure and behavior of Next.js applications using _app.js and _document.js files.
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The Custom App feature, defined in the _app.js file, is essentially the backbone of Next.js applications. It serves as the main entry point for initializing pages. The primary purpose of _app.js is to enable global CSS imports, maintain state when navigating between pages, and insert shared components across all pages, such as layouts and navigation bars. This customization layer is crucial for when you need consistent behavior across all your pages or wish to pass down props to every page in your application. For example, integrating global state management tools like Redux or Context API becomes streamlined with _app.js. It essentially acts as the wrapper around all your page components, providing a centralized place to manage...