RRC 4.0.5 Project Properties > Attribute Data Types > ArtifactFormats includes WrapperResource/file but you cannot pick it. What is it?

Examined RRC 4.0.5 because a customer created some "pic" type artifacts with format of "File".

RRC 4.0.5 Project Properties > Attribute Data Types > "ArtifactFormats" includes

WrapperResource  File  http://jazz.net/ns/rm#WrapperResource  

However, if you attempt to choose that option on any Format pull-down for any Artifacts either system-defined or user-defined, you cannot chose that.

I have a customer who has created some images with "Pic"/"File" for Artifact Type/Artifact Format, and others with "Pic"/"Text". I cannot seem to create more using the "File" format.

However, images embedded in the richText attribute of an artifact which have these attributes will successfully be pulled into an RPE report. Those other images will not.

Please explain the use of the WrapperResource (is it obsolete, hidden?)