When the try/catch block is unable to catch an error.
Correct:
When the try/catch block is unable to catch an error.
Explanation: Answer option D is correct.
The set_exception_handler() function is used to set a default exception handler if a try/catch block is unable to catch an error. The syntax of the set_exception_handler() function is as follows:
set_exception_handler(exception_function)
where the exception_function parameter specifies the function to be called when an uncaught exception occurs. It must be defined before calling the set_exception_handler() function.
Answer option A is incorrect. The set_error_handler() function is used to set a user-defined function to handle errors. This function allows a user to handle errors during runtime. The syntax of the set_error_handler() function is as follows:
set_error_handler(error_function, error_types)
where error_function specifies the function to be run at errors, and the error_types parameter specifies on which errors report levels the user-defined error will be shown. The default error level is "E_ALL".
Answer option B is incorrect. The restore_error_handler() function restores the previous error handler function.
Answer option C is incorrect. The trigger_error() function is used to generate a user-level error/warning/notice message.