IFClite TypeScript API
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    Variable IFC_BUILDING_STOREY_ELEVATION_INDEXConst

    IFC_BUILDING_STOREY_ELEVATION_INDEX: 9

    Attribute index of IfcBuildingStorey.Elevation, the same in IFC2X3 and IFC4:

    [0] GlobalId   [1] OwnerHistory  [2] Name             [3] Description
    [4] ObjectType [5] ObjectPlacement [6] Representation [7] LongName
    [8] CompositionType [9] Elevation

    Getting this wrong is silent: slots 7 and 8 hold a string and an enum, so an off-by-one read yields "no elevation" and the UI shows 0 rather than failing. The server's extract_elevation_if_storey (Rust) must stay in step with this.