<li><code>item</code>: the item being manipulated</li>
<li><code>callback</code>: a callback function which must be invoked to report back. The callback must be invoked as <code>callback(item | null)</code>. Here, <code>item</code> can contain changes to the passed item. When invoked as <code>callback(null)</code>, the action will be cancelled.</li>
<li><code>callback</code>: a callback function which must be invoked to report back. The callback must be invoked as <code>callback(item | null)</code>. Here, <code>item</code> can contain changes to the passed item. Parameter `item` typically contains fields `content`, `start`, and optionally `end`. The type of `start` and `end` is determined by the DataSet type configuration and is `Date` by default. When invoked as <code>callback(null)</code>, the action will be cancelled.</li>