Divisions define the grid orientation (whether the direction of the grid cells and mullions is horizontal or vertical) and the division type (number and size of cells).
After you define a division, you can assign it to the primary grid or to nested grids. Nested grids are created by selecting Nested Grid as the cell assignment.

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 Door/Window Assembly Styles. 
  
  
 . The name of the grid you select is displayed in the table under the Division Assignment row.