CRA stands for Create React App, which is a boilerplate for creating React applications. It provides a pre-configured setup for building, testing, and deploying React applications, allowing developers to focus on writing code rather than setting up the build toolchain. Some benefits of using CRA include easy setup, automatic configuration, and a built-in development server.

Error boundaries were not supported in React v15. Error handling in React v15 was less robust and could lead to the entire application crashing if an error occurred during rendering.

Route-based code splitting is a technique for splitting code based on the location of the component in the application. Route-based code splitting allows components to be loaded on-demand based on the user's navigation, reducing the initial load time of the application. Route-based code splitting is typically used with libraries like React Router to enable on-demand loading of code.

In React, you can use the dangerouslySetInnerHTML prop to set the inner HTML of a component. The dangerouslySetInnerHTML prop is used to bypass React's built-in sanitization and allow arbitrary HTML to be injected into a component. However, this should be used with caution, as it can pose a security risk.

React Hooks were introduced based on community proposals and discussions, as well as official React documentation and blog posts. They were also presented and discussed at React conferences and meetups.

Stateful components, also known as class components, are components that maintain state. Stateful components are useful for creating more complex UI components that need to maintain state, but they are more difficult to test than stateless components.

Whether or not to use Redux to manage state in a React application depends on the complexity and size of the application. For small and simple applications, it may be sufficient to use React's internal state management. However, for larger and more complex applications, Redux can be a helpful tool for managing application state.

The ref argument is only available for class components in React. Function components do not have an instance, so refs cannot be attached to them. Refs can be attached to DOM elements, class components, and functional components that are created using the forwardRef() method.

In React, the "setState" method is used to update component state, and it merges the new state with the old state. The "replaceState" method is similar, but it overwrites the old state completely with the new state. However, "replaceState" is deprecated in React and should not be used. Instead, you should use the "setState" method to update state in a React component.

In Create React App, you can use HTTPS instead of HTTP by setting the "HTTPS=true" environment variable. This will start the development server with HTTPS enabled, and will allow you to test your application with SSL/TLS encryption.