This option sets the default date format the calendar icon will use on a date widget. In many cases the date format is specified directly on the date widget, but if it is not specified, the default date format will be used.
Example:
The following line sets the default date format to USA with 4 digit year
pui.defaultDateFormat="MM/DD/YYYY";
If this option is not specified it will default to "MM/DD/YY"
Where do you save this configuration option? Here.