code: def _add_notes_slide_part(cls, package, slide_part, notes_master_part):
          
          partname = package.next_partname('/ppt/notesSlides/notesSlide%d.xml')
          content_type = CT.PML_NOTES_SLIDE
          notes = CT_NotesSlide.new()
          notes_slide_part = NotesSlidePart(
              partname, content_type, notes, package
          )
          notes_slide_part.relate_to(notes_master_part, RT.NOTES_MASTER)
          notes_slide_part.relate_to(slide_part, RT.SLIDE)
          return notes_slide_part
docs: Create and return a new notes slide part that is fully related, but
          has no shape content (i.e. placeholders not cloned).