These docs are for an old release.
Info on upgrading to version 2/3
dayNamesShort 1.3
Abbreviated names of days-of-week.
Array, default:
['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat']
Prior to version 1.3, this was possible by setting $.fullCalendar.dayAbbrevs