These docs are for an old release.
Info on upgrading to v4
drop
Called when a valid external jQuery UI draggable has been dropped onto the calendar.
function( date, jsEvent, ui, resourceId ) { }
date holds the Moment of where the draggable was dropped. It will either have a time, or be ambiguously-timed, depending on whether it was dropped on an all-day area or not.
jsEvent holds the jQuery event, with information like mouse coordinates.
ui holds the jQuery UI information.
resourceId will be populate if dropped on a Scheduler resource.
this holds the DOM element that has been dropped.
To see this callback function in action, view the droppable article or see this live demo.