Date format used for selected date values in calendar.

Date format examples:

* mm/dd/yy * dd-mm-yy

Note: yy is equivalent to 4 digit years!

The following format rules apply (from ui.datepicker.js):

d - day of month (no leading zero)
dd - day of month (two digit)
D - day name short
DD - day name long
m - month of year (no leading zero)
mm - month of year (two digit)
M - month name short
MM - month name long
y - year (two digit)
yy - year (four digit)
'...' - literal text '' - single quote