Structured IFC value containers indexed by position or time.

A table indexes values by row and column; a time series indexes them by time. Neither carries domain meaning of its own: both bottom out in lists of IfcValue, and both appear side by side in the schema's own IfcMetricValueSelect and IfcObjectReferenceSelect.

Cells are the caller's to type

A cell is an IfcValue: a SELECT over measure types. 4.2 and IFCLENGTHMEASURE(4.2) are different files, and only the second can be converted or compared dimensionally. This crate never invents a measure; the caller passes a Value and chooses.

Derived attributes are not stored

IfcTable DERIVEs three counts from its rows. STEP writes a derived attribute as *, not as a number, so they are emitted as [ifc_model::Value::Derived] and never computed into the file.