Insert an element with an ID one of these ways:
Split an element with an ID.
Paste or drag&drop an element with an ID into a scope which already has an element with the same ID value.
In these cases, the ID value of the newly-inserted element is automatically added a suffix _1, _2, and so on.
Join elements with IDs.
When you join two elements, the ID value of the first element is used for the joint element.
If the first element has no ID, the joint element will also have no ID.
To enable the maintenance of DITA ID uniqueness within a map, you must first specify the ID value of the map itself.