Relation pm#descr_in__descrin (?,pm#description_container)  when a thing t has a description stored in a description container dc, there is a relation pm#descr_in from t to dc
  supertype:  pm#file_or_file_element
  subtype:  pm#descr_container__description_support___descr_support (pm#description,pm#description_container)  permits to associate a statement with an object on which it is represented