BTW:

Travis fails on this:

There were 2 errors:
1) JFormFieldCalendarTest::testGetInputAttributes with data set "normal" (array('myCalendarElement', 'myCalendarId', 'myValue', '%m-%Y-%d', 25, 45, 'myClass', true, false, '', ''), array('myValue', 'myCalendarElement', 'myCalendarId', '%m-%Y-%d', array(25, 45, 'myClass', 'readonly')))
Exception: DateTime::__construct(): Failed to parse time string (myValue) at position 0 (m): The timezone could not be found in the database
/home/travis/build/joomla/joomla-cms/libraries/joomla/date/date.php:106
/home/travis/build/joomla/joomla-cms/libraries/joomla/factory.php:530
/home/travis/build/joomla/joomla-cms/libraries/joomla/form/fields/calendar.php:172
/home/travis/build/joomla/joomla-cms/tests/unit/core/reflection/reflection.php:79
/home/travis/build/joomla/joomla-cms/tests/unit/suites/libraries/joomla/form/fields/JFormFieldCalendarTest.php:318
2) JFormFieldCalendarTest::testGetInput
Exception: DateTime::__construct(): Failed to parse time string (value) at position 0 (v): The timezone could not be found in the database
/home/travis/build/joomla/joomla-cms/libraries/joomla/date/date.php:106
/home/travis/build/joomla/joomla-cms/libraries/joomla/factory.php:530
/home/travis/build/joomla/joomla-cms/libraries/joomla/form/fields/calendar.php:172
/home/travis/build/joomla/joomla-cms/libraries/joomla/form/field.php:393
/home/travis/build/joomla/joomla-cms/libraries/joomla/form/fields/calendar.php:73
/home/travis/build/joomla/joomla-cms/tests/unit/suites/libraries/joomla/form/fields/JFormFieldCalendarTest.php:523
--
There was 1 failure:
1) JFormFieldCalendarTest::testGetInputAttributes with data set "value_is_now" (array('myCalendarElement', 'myCalendarId', 'NOW', '%Y-%m-%d', 25, 45, true, 'This is my onchange value', ''), array('strftime('%Y-%m-%d')', 'myCalendarElement', 'myCalendarId', '%Y-%m-%d', array(25, 45, 'disabled', 'This is my onchange value')))
Expectation failed for method name is equal to <string:calendar> when invoked 1 time(s)
Parameter 0 for invocation calendarHandler::calendar('2015-01-04 12:12:52', 'myCalendarElement', 'myCalendarId', '%Y-%m-%d', Array (...)) does not match expected value.
Failed asserting that two strings are equal.
--- Expected
+++ Actual
@@ @@
-'2015-01-04'
+'2015-01-04 12:12:52'
/home/travis/build/joomla/joomla-cms/libraries/cms/html/html.php:236
/home/travis/build/joomla/joomla-cms/libraries/cms/html/html.php:104
/home/travis/build/joomla/joomla-cms/libraries/joomla/form/fields/calendar.php:201
/home/travis/build/joomla/joomla-cms/tests/unit/core/reflection/reflection.php:79
/home/travis/build/joomla/joomla-cms/tests/unit/suites/libraries/joomla/form/fields/JFormFieldCalendarTest.php:318

https://travis-ci.org/joomla/joomla-cms/jobs/45843122

travis is more complicated part

maybe this can help travis? @Fedik mbabker@23ec2d7

I wonder if that has to be a feature in core. The usecase is probably quite limited and it would be easy for an extension to extend that field and implement such advanced methods.

@Bakual I wonder why it still not in the core
and why we support now but nothing more ...

@zero-24 thanks I will try

ok, test fixed.
and I added one more test case for now +1 year, so i would count it as one successful tester

@test
Looks like working, including with custom calendars as the one for Persian.
Do we need it is another story indeed.

Would have been very useful for me this week

Thank you for your suggestion but it has been decided that this is not something that will be included in the core of Joomla.