Typically for IFC export, this represents the lower and upper elevations for split wall and column geometry. 
Namespace: Autodesk.Revit.DB.IFC
Assembly: RevitAPIIFC (in RevitAPIIFC.dll) Version: 24.0.0.0 (24.0.0.0)
Since:  2013 
Syntax
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Remarks
 It contains two double values representing the starting and ending values as a range. 
Inheritance Hierarchy
SystemObject
Autodesk.Revit.DB.IFCIFCRange
Autodesk.Revit.DB.IFCIFCRange