Item Attachment Deleting – This occurs while an attachment is being removed from an item.
Item Checked In – This occurs after an item is checked in.
In my case I was changing the value of a custom property named CMIs Secret, so if that property was the same in before Properties as in after Properties (the values before and after the save) I should go on with the update, otherwise not.
This was the method I created: It checks if the property exists at all (it doesn’t if it is an Item Added-event and the property is custom made) and if it differs.
They are used to perform some custom action before an event occurs.