code: def _is_pptx_package(prs_part):
      
      valid_content_types = (
          CT.PML_PRESENTATION_MAIN,
          CT.PML_PRES_MACRO_MAIN,
      )
      return prs_part.content_type in valid_content_types
docs: Return |True| if *prs_part* is a valid main document part, |False|
      otherwise.