Dimension-Driven Cells
Cells have many uses: They can save time drawing repeated details, make it easy to update details throughout a design, provide uniformity in a project, and so on. Although they can be modified, most cells are placed as static parts of a DGN file.
A dimension-driven cell has special "intelligence." It is not static, but dynamically changes based on relationships that were defined when it was created. A cell in the DGN file that is based on a dimension-driven cell is called a derived cell. Derived Cells can be placed with the Dimension-Driven Design dialog.