It describes overall how "deep" the view is.
Elements falling below the "bottom" of the primary view range but above the "level" in the view depth setting will be shown using the <beyond> line style, with a few exceptions for specific categories/conditions.
From the Help:
Elements within the view depth are drawn using the <Beyond> line style regardless of the element's category.
Exceptions: Floors, structural floors, stairs, and ramps located outside the view range use an adjusted range that is 4 feet (about 1.22 meters) below the bottom of the primary range. Within this adjusted range, the elements are drawn using the projection line weight for the category. If they exist outside this adjusted range but within the view depth, these elements are drawn using the <Beyond> line style.
You will find this section about 1/2 way down the page.
http://help.autodesk.com/view/RVT/2018/ENU/?guid=GUID-58711292-AB78-4C8F-BAA1-0855DDB518BF
loboarch,
Please don't get me started on the "Exceptions" crap. Those hardwired exceptions really irritate me.
Let EVERY category follow the default display behaviors. I'll set up overrides if I want unique behavior.
I love Revit overall, but hardwired exceptions is one of the dumbest bits.
Allows you to control what you can see by cutting plans at different levels.
Not very helpful when you want to see objects that you may have placed at different heights - clerestory windows being an example. In that case I like to use Plan Regions.
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