code: def core_properties(self):
          
          try:
              return self.part_related_by(RT.CORE_PROPERTIES)
          except KeyError:
              core_props = CorePropertiesPart.default()
              self.relate_to(core_props, RT.CORE_PROPERTIES)
              return core_props
docs: Instance of |CoreProperties| holding the read/write Dublin Core
          document properties for this presentation. Creates a default core
          properties part if one is not present (not common).