The extraction functionality allows for extracting a selected part of an activity diagram to a newly created diagram. After extraction, in the source diagram, a call behavior action is created instead of the extracted part. That is, the call behavior action is a referencing element that references the newly created activity diagram.
As you can see in the example, during extraction, the selected part of the activity diagram is moved to the newly created Review Items activity diagram. In the source diagram, a Review Items call behavior action is created in place of the selected elements.