PositionChanged

This rule is triggered after a successful position change.
This happens :

• when a user clicks on a different item in a datagrid
• when the Position property is changed by code
• after the Retrieved event rule is executed.

See this article to learn how the Retrieved event rules changes the position.
See this article for more information on event rules execution order.

Item versus DatasourceCurrent

The Item property does not exist in this rule.
DatasourceCurrent refers to the item at the new position.

To know more on the difference between the Item and DatasourceCurrent properties in an UI view event rule, you can check this article.