[1] UTS #35: Unicode LDML: Dates ( 版) http://www.unicode.org/reports/tr35/tr35-dates.html#Date_Field_Symbol_Table
[3] UTS #35: Unicode LDML: Dates ( 版) http://www.unicode.org/reports/tr35/tr35-dates.html#Date_Format_Patterns
[4] Date/Time Patterns - CLDR - Unicode Common Locale Data Repository () http://cldr.unicode.org/translation/date-time-patterns
[7] Apple の Cocoa (Mac OS X や iOS で使われている) で実装され、 Objective-C や Swift のようなプログラミング言語で使われています。 >>6
To specify a custom fixed format for a date formatter, you use setDateFormat:. The format string uses the format patterns from the Unicode Technical Standard #35.
The supported date and time format patterns listed here are expressed in terms of the date field symbols defined in [UAX35]. These formats must be recognised by implementations and must be interpreted as defined in that specification. Implementations may additionally recognise other date format patterns. Implementations must issue a warning if the date format pattern is invalid or not recognised and proceed as if no date format pattern had been provided.