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Determines the text that will be displayed on the calendar’s column headings.

This settings has been renamed to columnHeaderFormat.

format string, default:

'ddd'     // like 'Mon', for month view
'ddd M/D' // like 'Mon 9/7', for week views
'dddd'    // like 'Monday', 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.