What is the correct way to incorporate validation into error handling?

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The correct way to incorporate validation into error handling is to perform validation checks on user input or data before processing it, and if the validation fails, throw an appropriate error with a clear message describing the issue. This error should be caught and handled properly in a way that provides feedback to the user, such as displaying an error message explaining what went wrong and how it can be fixed. Additionally, any errors that may occur during processing should also be caught and handled appropriately to ensure the application remains stable and functional.