Building a special structure
The special structures will never override the original product structure of the Article (ART), and will always be specific for the document where you made the special structure.
Two methods for creating a special structure
Enter the specific document line and pressing F12, or right click, to open the action menu. Choose the option Copy structure from ART. This presumes the structure is not empty. You will see the icon for special structure showing up and the special structure has been made based on the original product structure.
Enter the specific document line and pressing F12, or right click, to open the action menu. Choose the option Create Special Structure. This presumes the article base for the structure is not empty, but also different enough that it is impractical to use as a base. You will see the icon for special structure showing up and an empty special structure has been created.