Determines how the day names are displayed in the pop-up calendar.
This is a string value which can be set in the following ways:
1char: uses the first letter of the day. Note that this starts with the numeral '1', not a lower-case 'L'.
short: uses two characters to represent the day name.
medium: uses the standard three-character day names
long: displays the full name based on user locale.
Default is long.