[TASK] Add documentation for DatePicker formats

This patch adds some documentation for the DatePicker
form element and the available date formats.

Resolves: #82508
Releases: master, 8.7
Change-Id: I1277c024112633ec7e38f4c8cbe30efb97375ce3
Reviewed-on: https://review.typo3.org/56978


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>
Reviewed-by: Ralf Zimmermann <ralf.zimmermann@tritum.de>
Tested-by: Ralf Zimmermann <ralf.zimmermann@tritum.de>

typo3/sysext/form/Documentation/Config/proto/formElements/formElementTypes/DatePicker/properties/dateFormat.rst

@@ -40,4 +40,36 @@ properties.dateFormat
       ToDo
 
 :aspect:`Description`
-      The datepicker time format.
\ No newline at end of file
+      The datepicker time format.
+      The following date formats are allowed:
+
+      **Day**
+
+      ================ ==================================================================
+      Format character Description
+      ================ ==================================================================
+      d                Day of the month, two digits with leading zeros
+      D                A textual representation of a day, three letters
+      j                Day of the month without leading zeros
+      l                A full textual representation of the day of the week
+      ================ ==================================================================
+
+      **Month**
+
+      ================ ==================================================================
+      Format character Description
+      ================ ==================================================================
+      F                A full textual representation of a month, such as January or March
+      m                Numeric representation of a month, with leading zeros
+      M                A short textual representation of a month, three letters
+      n                Numeric representation of a month, without leading zeros
+      ================ ==================================================================
+
+      **Year**
+
+      ================ ==================================================================
+      Format character Description
+      ================ ==================================================================
+      Y                A full numeric representation of a year, four digits
+      y                A two digit representation of a year
+      ================ ==================================================================
\ No newline at end of file