To Place a Drawing Boundary by Element

Select the Place Drawing Boundary tool.
(Optional) Select a detailing symbol style.
Select By Element.
Select the element that will form the boundary of the drawing boundary.
Enter a data point to define the location of the annotation of the drawing boundary.

Placing a Drawing Boundary by Element

If you place a drawing boundary in a DGNLib file, it can be used for placing named boundaries in your model.