Relation rst#cause (description_content/medium/container,description_content/medium/container)  not a subtype of pm#cause since pm#cause connects situations
  exclusion:  circumstance  solution  elaboration  effect  definition  comparison  means  condition  otherwise  interpretation  restatement  summary  theme  contrast
  supertype:  subject_matter_rhetorical_relation  connect to details for making a better description
  subtype:  volitional_cause (description_content/medium/container,description_content/medium/container)  cause of the described intended situation
  subtype:  non-volitional_cause (description_content/medium/container,description_content/medium/container)  cause of the described not intended situation
  subtype:  purpose (description_content/medium/container,description_content/medium/container)  situation that the described action is intended to reach