Create title-format documentation

a complete description of all date fomats and how to use them could be very useful to users!

Not documentation, but maybe this gets you through in the meantime:
(source Logseq/app-0.10.8/resources/app/js/cljs_time/format.cljs)

  Map of ISO 8601 and a single RFC 822 formatters that can be used
  for parsing and, in most cases, printing.
  Note: due to current implementation limitations, timezone information
  cannot be kept. Although the correct offset will be applied to UTC
  time if supplied.

  The pattern syntax is mostly compatible with java.text.SimpleDateFormat -
  time zone names cannot be parsed and a few more symbols are supported. All
  ASCII letters are reserved as pattern letters, which are defined as follows:

    Symbol  Meaning                      Presentation  Examples
    ------  -------                      ------------  -------
    G       era                          text          AD
    C       century of era (>=0)         number        20
    Y       year of era (>=0)            year          1996

    x       weekyear                     year          1996
    w       week of weekyear             number        27
    e       day of week                  number        2
    E       day of week                  text          Tuesday; Tue

    y       year                         year          1996
    D       day of year                  number        189
    M       month of year                month         July; Jul; 07
    d       day of month                 number        10

    a       halfday of day               text          PM
    K       hour of halfday (0~11)       number        0
    h       clockhour of halfday (1~12)  number        12

    H       hour of day (0~23)           number        0
    k       clockhour of day (1~24)      number        24
    m       minute of hour               number        30
    s       second of minute             number        55
    S       fraction of second           number        978
    a       meridiem                     text          am; pm
    A       meridiem                     text          AM; PM

    z       time zone                    text          Pacific Standard Time; PST
    Z       time zone offset/id          zone          -0800; -08:00; America/Los_Angeles

    '       escape for text              delimiter
    ''      single quote                 literal       '

    cljs-time additions:
    ------  -------                      ------------  -------
    Symbol  Meaning                      Presentation  Examples
    ------  -------                      ------------  -------
    o       ordinal suffix               text          st nd rd th (E.G., 1st, 2nd, 3rd, 4th)

  The count of pattern letters determine the format.

  **Text:** If the number of pattern letters is 4 or more, the full form is used;
  otherwise a short or abbreviated form is used if available.

  **Number:** The minimum number of digits. Shorter numbers are zero-padded to this

  **Year:** Numeric presentation for year and weekyear fields are handled
  specially. For example, if the count of `y` is 2, the year will be displayed
  as the zero-based year of the century, which is two digits.

  **Month:** 3 or over, use text, otherwise use number.

  **Zone:** `Z` outputs offset without a colon, `ZZ` outputs the offset with a
  colon, `ZZZ` or more outputs the zone id.

  **Zone names:** Time zone names ('z') cannot be parsed.

  Any characters in the pattern that are not in the ranges of `['a'..'z']` and
  `['A'..'Z']` will be treated as quoted text. For instance, characters like `:`,
  `.`, `<space>`, `#` and `?` will appear in the resulting time text even they are
  not embraced within single quotes."}
    {:basic-date (formatter "yyyyMMdd")
     :basic-date-time (formatter "yyyyMMdd'T'HHmmss.SSSZ")
     :basic-date-time-no-ms (formatter "yyyyMMdd'T'HHmmssZ")
     :basic-ordinal-date (formatter "yyyyDDD")
     :basic-ordinal-date-time (formatter "yyyyDDD'T'HHmmss.SSSZ")
     :basic-ordinal-date-time-no-ms (formatter "yyyyDDD'T'HHmmssZ")
     :basic-time (formatter "HHmmss.SSSZ")
     :basic-time-no-ms (formatter "HHmmssZ")
     :basic-t-time (formatter "'T'HHmmss.SSSZ")
     :basic-t-time-no-ms (formatter "'T'HHmmssZ")
     :basic-week-date (formatter "xxxx'W'wwe")
     :basic-week-date-time (formatter "xxxx'W'wwe'T'HHmmss.SSSZ")
     :basic-week-date-time-no-ms (formatter "xxxx'W'wwe'T'HHmmssZ")
     :date (formatter "yyyy-MM-dd")
     :date-element-parser (not-implemented 'dateElementParser)
     :date-hour (formatter "yyyy-MM-dd'T'HH")
     :date-hour-minute (formatter "yyyy-MM-dd'T'HH:mm")
     :date-hour-minute-second (formatter "yyyy-MM-dd'T'HH:mm:ss")
     :date-hour-minute-second-fraction (formatter "yyyy-MM-dd'T'HH:mm:ss.SSS")
     :date-hour-minute-second-ms (formatter "yyyy-MM-dd'T'HH:mm:ss.SSS")
     :date-opt-time (not-implemented 'dateOptionalTimeParser)
     :date-parser (not-implemented 'dateParser)
     :date-time (formatter "yyyy-MM-dd'T'HH:mm:ss.SSSZZ")
     :date-time-no-ms (formatter "yyyy-MM-dd'T'HH:mm:ssZZ")
     :date-time-parser (not-implemented 'dateTimeParser)
     :hour (formatter "HH")
     :hour-minute (formatter "HH:mm")
     :hour-minute-second (formatter "HH:mm:ss")
     :hour-minute-second-fraction (formatter "HH:mm:ss.SSS")
     :hour-minute-second-ms (formatter "HH:mm:ss.SSS")
     :local-date-opt-time (not-implemented 'localDateOptionalTimeParser)
     :local-date (not-implemented 'localDateParser)
     :local-time (not-implemented 'localTimeParser)
     :ordinal-date (formatter "yyyy-DDD")
     :ordinal-date-time (formatter "yyyy-DDD'T'HH:mm:ss.SSSZZ")
     :ordinal-date-time-no-ms (formatter "yyyy-DDD'T'HH:mm:ssZZ")
     :time (formatter "HH:mm:ss.SSSZZ")
     :time-element-parser (not-implemented 'timeElementParser)
     :time-no-ms (formatter "HH:mm:ssZZ")
     :time-parser (formatter 'timeParser)
     :t-time (formatter "'T'HH:mm:ss.SSSZZ")
     :t-time-no-ms (formatter "'T'HH:mm:ssZZ")
     :week-date (formatter "xxxx-'W'ww-e")
     :week-date-time (formatter "xxxx-'W'ww-e'T'HH:mm:ss.SSSZZ")
     :week-date-time-no-ms (formatter "xxxx-'W'ww-e'T'HH:mm:ssZZ")
     :weekyear (formatter "xxxx")
     :weekyear-week (formatter "xxxx-'W'ww")
     :weekyear-week-day (formatter "xxxx-'W'ww-e")
     :year (formatter "yyyy")
     :year-month (formatter "yyyy-MM")
     :year-month-day (formatter "yyyy-MM-dd")
     :rfc822 (formatter "EEE, dd MMM yyyy HH:mm:ss Z")
     :mysql (formatter "yyyy-MM-dd HH:mm:ss")})

thanks @etc
that’s a really good start to know which letters to use

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