Function pm#format (description_content/medium/container -> description_content/medium/container)
  supertype:  Format (description_content/medium/container -> entity)  to specify the physical or digital manifestation of a resource; in WebKB, this relation type SHOULD NOT BE USED; see pm#format, pm#description_instrument and pm#descr instead
     supertype:  relation_from_description_content/medium/container (description_content/medium/container,*)
        supertype:  relation_from/to_thing_of_common_kind (*)  this type permits to categorize relations according to their signatures and hence offers (i) a concise way to set essential exclusion relations, and (ii) a systematic and easy-to-follow categorization
           >part of:  relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type