$date_string = '07/17/2021'; $format = 'm/d/Y'; $is_valid = date_create_from_format($format, $date_string) !== false;In this example, the $date_string variable contains the date string to be validated, and the $format variable specifies the expected format of the date string (in this case, "month/day/year"). The date_create_from_format function is used to create a new date object from the provided string, according to the specified format. If the format is valid, the resulting date object will not be false, indicating that the date is valid. The isDate validation function is part of the PHP core, and does not require any additional libraries or packages. However, there are many third-party libraries and packages available that can provide more robust date validation functionality, as well as other date-related functions and utilities. Some popular options include the Carbon library, the DateInterval class, and the DateTimeImmutable class.