Tests if the supplied date is valid for the Gregorian calendar.

function wp_checkdate( $month, $day, $year, $source_date ) {
	/**
	 * Filters whether the given date is valid for the Gregorian calendar.
	 *
	 * @since 3.5.0
	 *
	 * @param bool   $checkdate   Whether the given date is valid.
	 * @param string $source_date Date to check.
	 */
	return apply_filters( 'wp_checkdate', checkdate( $month, $day, $year ), $source_date );
}