These docs are for an old release.
Info on upgrading to v4
titleFormat
Determines the text that will be displayed in the header’s title.
format string, default:
'MMMM YYYY' // like 'September 2009', for month view
'MMM D YYYY' // like 'Sep 13 2009', for week views
'MMMM D YYYY' // like 'September 8 2009', for day views
As noted above, each view has a specific default. Get fine-tuned control with View-Specific Options. A single string alone will set the value for all views.
The default values will change based on the current locale.