This rule classifies/colors the faces of a mass by their orientation.
This rule colors parts of a multipatch based on the orientation of the faces. Vertical faces are colored beige, flat faces are colored grey, sloped faces are colored red. This is a good reference when editing a multipatch in ArcGIS Pro as to how the multipatch will be textured by the built in procedural symbology, or with an rule package (RPK) that textures buildings or gives them facades (such as the Building Shell with Detail rule: http://bit.ly/ROTW_BSwD).
You can see a video of the rule working in CityEngine and ArcGIS Pro here: https://youtu.be/To2YoT803yw
Give CityEngine a try with this free 30-day trial: http://bit.ly/EsriCETrialLink