The format of the outputted date string. See the formatting options below. There are also several predefined date constants that may be used instead, so for example DATE_RSS contains the format string 'D, d M Y H:i:s'.
2021 May 18
2021 May 18
ISO-8601 week-numbering year. This has the same value as Y, except that if the ISO week number (W) belongs to the previous or next year, that year is used instead.
2021 May 18
Timezone offset in seconds. The offset for timezones west of UTC is always negative, and for those east of UTC is always positive.