Task
 
Choose popular date libraries used by your language and show the   epoch   those libraries use.

A demonstration is preferable   (e.g. setting the internal representation of the date to 0 ms/ns/etc.,   or another way that will still show the epoch even if it is changed behind the scenes by the implementers),   but text from (with links to) documentation is also acceptable where a demonstration is impossible/impractical.

For consistency's sake, show the date in UTC time where possible.



Related task

   Date format


/*REXX program displays the number of days since the epoch for the DATE function (BIF). */
 
say '     today is: '  date()                    /*today's is format:     mm MON YYYY   */
 
days=date('Basedate')                            /*only the first char of option is used*/
say right(days, 40)         " days since the REXX base date of January 1st, year 1"
 
say ' and today is: '  date(, days, "B")         /*it should still be today (µSec later)*/
                    /*   ↑                ┌───◄─── This BIF (Built-In Function) is only */
                    /*   └─────────◄──────┘        for  newer  versions of  REXX  that  */
                    /*                             support the  2nd and 3rd  arguments. */