* Returns the UNIX timestamp for the current date.
     *
     * @return int
     */
    public function unix();

    /**
     * @alias to
     *
     * Get the difference in a human readable format in the current locale from an other
     * instance given (or now if null given) to current instance.
     *
     * @param Carbon|\DateTimeInterface|string|array|null $other   if array passed, will be used as parameters array, see $syntax below;
     *                                                             if null passed, now will be used as comparison reference;
     *                                                             if any other type, it will be converted to date and used as reference.
     * @param int|array                                   $syntax  if array passed, parameters will be extracted from it, the array may contains:
     *                                                             - 'syntax' entry (see below)
     *                                                             - 'short' entry (see below)
     *                                                             - 'parts' entry (see below)
     *                                                             - 'options' entry (see below)
     *                                                             - 'join' entry determines how to join multiple parts of the string
     *                                                             `  - if $join is a string, it's used as a joiner glue
     *                                                             `  - if $join is a callable/closure, it get the list of string and should return a string
     *                                                             `  - if $join is an array, the first item will be the default glue, and the second item
     *                                                             `    will be used instead of the glue for the last item
     *                                                             `  - if $join is true, it will be guessed from the locale ('list' translation file entry)
     *                                                             `  - if $join is missing, a space will be used as glue
     *                                                             - 'other' entry (see above)
     *                                                             if int passed, it add modifiers:
     *                                                             Possible values:
     *                                                             - CarbonInterface::DIFF_ABSOLUTE          no modifiers
     *                                                             - CarbonInterface::DIFF_RELATIVE_TO_NOW   add ago/from now modifier
     *                                                             - CarbonInterface::DIFF_RELATIVE_TO_OTHER add before/after modifier
     *                                                             Default value: CarbonInterface::DIFF_ABSOLUTE
     * @param bool                                        $short   displays short format of time units
     * @param int                                         $parts   maximum number of parts to display (default value: 1: single unit)
     * @param int                                         $options human diff options
     *
     * @return string
     */
    public function until($other = null, $syntax = null, $short = false, $parts = 1, $options = null);

    /**
     * @deprecated To avoid conflict between different third-party libraries, static setters should not be used.
     *             You should rather use the ->settings() method.
     *             Or you can use method variants: addMonthsWithOverflow/addMonthsNoOverflow, same variants
     *             are available for quarters, years, decade, centuries, millennia (singular and plural forms).
     * @see settings
     *
     * Indicates if months should be calculated with overflow.
     *
     * @param bool $monthsOverflow
     *
     * @return void
     */
    public static function useMonthsOverflow($monthsOverflow = true);

    /**
     * @deprecated To avoid conflict between different third-party libraries, static setters should not be used.
     *             You should rather use the ->settings() method.
     * @see settings
     *
     * Enable the strict mode (or disable with passing false).
     *
     * @param bool $strictModeEnabled
     */
    public static function useStrictMode($strictModeEnabled = true);

    /**
     * @deprecated To avoid conflict between different third-party libraries, static setters should not be used.
     *             You should rather use the ->settings() method.
     *             Or you can use method variants: addYearsWithOverflow/addYearsNoOverflow, same variants
     *             are available for quarters, years, decade, centuries, millennia (singular and plural forms).
     * @see settings
     *
     * Indicates if years should be calculated with overflow.
     *
     * @param bool $yearsOverflow
     *
     * @return void
     */
    public static function useYearsOverflow($yearsOverflow = true);

    /**
     * Set the instance's timezone to UTC.
     *
     * @return static
     */
    public function utc();

    /**
     * Returns the minutes offset to UTC if no arguments passed, else set the timezone with given minutes shift passed.
     *
     * @param int|null $offset
     *
     * @return int|static
     */
    public function utcOffset(int $offset = null);

    /**
     * Returns the milliseconds timestamps used amongst other by Date javascript objects.
     *
     * @return float
     */
    public function valueOf();

    /**
     * Get/set the week number using given first day of week and first
     * day of year included in the first week. Or use US format if no settings
     * given (Sunday / Jan 6).
     *
     * @param int|null $week
     * @param int|null $dayOfWeek
     * @param int|null $dayOfYear
     *
     * @return int|static
     */
    public function week($week = null, $dayOfWeek = null, $dayOfYear = null);

    /**
     * Set/get the week number of year using given first day of week and first
     * day of year included in the first week. Or use US format if no settings
     * given (Sunday / Jan 6).
     *
     * @param int|null $year      if null, act as a getter, if not null, set the year and return current instance.
     * @param int|null $dayOfWeek first date of week from 0 (Sunday) to 6 (Saturday)
     * @param int|null $dayOfYear first day of year included in the week #1
     *
     * @return int|static
     */
    public function weekYear($year = null, $dayOfWeek = null, $dayOfYear = null);

    /**
     * Get/set the weekday from 0 (Sunday) to 6 (Saturday).
     *
     * @param int|null $value new value for weekday if using as setter.
     *
     * @return static|int
     */
    public function weekday($value = null);

    /**
     * Get the number of weeks of the current week-year using given first day of week and first
     * day of year included in the first week. Or use US format if no settings
     * given (Sunday / Jan 6).
     *
     * @param int|null $dayOfWeek first date of week from 0 (Sunday) to 6 (Saturday)
     * @param int|null $dayOfYear first day of year included in the week #1
     *
     * @return int
     */
    public function weeksInYear($dayOfWeek = null, $dayOfYear = null);

    /**
     * Create a Carbon instance for yesterday.
     *
     * @param \DateTimeZone|string|null $tz
     *
     * @return static
     */
    public static function yesterday($tz = null);

    // </methods>
}