Element Documentation - NDR Question

It was a good meeting in Manhattan last week.  Mark Crawford did
a really good job overviewing CCTS 3.0.

I provided some comments on the NDR to Mike last week.  I started looking
closer at the UBL 2.0 schemas.  I found something that I found confusing.
Element declarations (ABIE and BBIE) do not have any documentation nodes
for them when they are defined.

A referred element does have a definition.  For example: