Expansion of options: "Allowed URL Characters"

You can customize the error page because it throws BadRequestException with the error code 400.

Create "error_400.php" in https://github.com/codeigniter4/CodeIgni...rrors/html

Note that if Excetions with the code 400 are thrown, the file is always used.
So you must take care of production or development environments.
See "error_404.php"
https://github.com/codeigniter4/CodeIgni...hp#L76-L80

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