The id of the base level of stairs on which the NumberSystem is placed.
Namespace: Autodesk.Revit.DB
Assembly: RevitAPI (in RevitAPI.dll) Version: 25.0.0.0 (25.0.0.0)
public LinkElementId PlacementLevelId { get; }
In multistory stairs, a stairs element could be a stair group or individual stair, this level could be the base level of group member or stairs element.