docs: def add_section_break(self):
          """Return `w:sectPr` element for new section added at end of document.
  
          The last `w:sectPr` becomes the second-to-last, with the new `w:sectPr` being an
          exact clone of the previous one, except that all header and footer references
          are removed (and are therefore now "inherited" from the prior section).
  
          A copy of the previously-last `w:sectPr` will now appear in a new `w:p` at the
          end of the document. The returned `w:sectPr` is the sentinel `w:sectPr` for the
          document (and as implemented, *is* the prior sentinel `w:sectPr` with headers
          and footers removed).
          """
          # ---get the sectPr at file-end, which controls last section (sections[-1])---
          sentinel_sectPr = self.get_or_add_sectPr()
          # ---add exact copy to new `w:p` element; that is now second-to last section---
          self.add_p().set_sectPr(sentinel_sectPr.clone())
          # ---remove any header or footer references from "new" last section---
          for hdrftr_ref in sentinel_sectPr.xpath("w:headerReference|w:footerReference"):
              sentinel_sectPr.remove(hdrftr_ref)
          # ---the sentinel `w:sectPr` now controls the new last section---
          return sentinel_sectPr