You can split a wall along a horizontal line in an elevation or a 3D view. After you split a wall, Vasari treats it as 2 separate walls, which means that you can modify one part independently of the other.
For example, in a 2-level building, suppose you snap the split to Level 2, and the top piece has a base constraint of Level 1. The lower wall has a height constraint of Level 2. If you split the walls at another point away from the levels, the lower wall has an explicit height constraint, while the top wall has a value for the base offset.
A temporary horizontal line displays on the wall when you place the cursor near vertical edges. If desired, you can snap to levels, so you split the wall evenly between levels.
Temporary horizontal line appearing
A permanent horizontal line displays on the wall indicating the split.
Permanent horizontal split