class RubyXL::Chartsheet

def attach_relationship(rid, rf)
  case rf
  when RubyXL::DrawingFile then store_relationship(rf) # TODO

  else store_relationship(rf, :unknown)
  end
end

def relationship_file_class
  RubyXL::SheetRelationshipsFile
end

def xlsx_path
  File.join('xl', 'chartsheets', "sheet#{file_index}.xml")
end