These docs are for an old release. Info on upgrading to v4
edit doc

Date Formatting Strings

Date formatting strings are used throughout the API and determine how a given Moment object is rendered to a string.

FullCalendar leverages MomentJS for most date-related operations including formatting dates:

See MomentJS’s formatting characters

However, FullCalendar has extended Moment’s functionality a bit by adding additional formatting characters:

Trenders "A" or "P" (one-letter, uppercase, for AM or PM)
trenders "a" or "p" (one-letter, lowercase, for AM or PM)
( ... )only renders the enclosed string if one or more non-zero digits

These formatting characters are only available to moments generated via the API as well as moments created with one of the special moment constructors.

Formatting ranges

Many parts of the API accept formatting strings for ranges, two dates that denote a start and end time. Some examples include titleFormat and timeFormat.

In this scenario, FullCalendar intelligently inserts a dash between the two dates, yielding something like "Sep 2 - 9 2013". Internally, formatRange is used for this.