A feature element is a generalization of all existence-dependent elements which modify the shape and appearance of the associated master element. The IfcFeatureElement offers the ability to handle shape modifiers as semantic objects within the IFC object model. 

In contrary to the aggregation, as used in IfcElementAssembly, that defines the aggregate as a container element, that has equally treated parts, the feature concept introduced by IfcFeatureElement defines the master element with subordinate parts as additions, or with voids or cut-outs as subtractions. 

As a subordinate part being fully dependent on the master element, the IfcFeatureElement has no independent containment relationship to the spatial structure.

• The SELFIfcElement.ContainedInStructure relationship should be NIL.