Sets the format for weekdays that appear across the top of the calendar.
Set the value to "None" to prevent display of the weekdays row.
The default value is "dddd" for the Data Calendar and "dd" for both the Input Date and the Date Picker elements. "dddd" shows the full weekday name, i.e "Monday", while "ddd" displays an abbreviated weekday name as "Mon". Use "dd" to display the weekday name as "M".