Ambiguity on whether or not object aggregates can have a body

According to the [element decomposition concept](https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/concepts/Object_Composition/Aggregation/Element_Decomposition/content.html) it says:

> By default the following constraints apply to an element being decomposed by Element Decomposition:
>
> Body Geometry — composite is constructed from the sum of the Body Geometry of the parts;
> the composite shall not have an own Body Geometry, body geometry is provided at the parts;
> the composite shall not have an own Material assignment, material is assigned to the parts.

However the page on IfcElementAssembly, very commonly used in steel assemblies, contradict this:

> The geometry of an [IfcElementAssembly](https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/lexical/IfcElementAssembly.htm) is generally formed from its components, in which case it does not need to have an explicit geometric representation. **In some cases it may be useful to also expose an own explicit representation of the aggregate.**

Note the sentence I marked in bold.

Also the Element Decomposition concept has this note but what is it referring to? I've never heard of a "Element Decomposition Required" subtemplate:

> Use the sub template Element Decomposition Required if any instance of the element is required to represent a composite with declared parts.

Read the Element Decomposition concept and the IfcElementAssembly lexical page linked in the issue, then trace the reference to the “Element Decomposition Required” subtemplate in the IFC4x3 documentation. Compare the stated rules and terminology, and document a resolved, consistent explanation of whether aggregate elements may have their own body geometry and what the subtemplate reference means.

Written by the indexing model from the issue text.