In MicroStation PowerDraft you can have an infinite number of reference attachments, and those attachments can have attachments, which in turn can have more attachments, and so on. This concept is called nesting. Nested references make it easy for you to attach and display multiple references, just by attaching a single, parent reference to a model.

When you are attaching references, you can control the manner in which nested references are to be attached to the model, or you can decide not to attach any nested references at all. If you do decide to include nested references when attaching a parent reference, you can control how many levels of nested references to attach to the model. This is called setting the nesting depth. The higher the number you set, the more certain you can be about including even the most deeply nested references when attaching a parent reference.

The Nested Attachments option menu on the Reference Attachment Properties dialog controls how nested references are handled when attaching a parent reference.