These docs are for an old release. Info on upgrading to v6
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eventDurationEditable

Allow events’ durations to be editable through resizing.

Boolean, default: true

You must enable the interaction plugin before using this setting. See code samples on the editable article

This option can be overridden on a per-source basis with the durationEditable Event Source Object option or on a per-event basis with the durationEditable Event Object option.