@property
    def nspfxs(self):
        def merge(seq, seq_2):
            for item in seq_2:
                if item in seq:
                    continue
                seq.append(item)

        nspfxs = self.local_nspfxs
        for child in self._children:
            merge(nspfxs, child.nspfxs)
        return nspfxs
A sequence containing each of the namespace prefixes appearing in
dataset/ETHPy150Open scanny/python-pptx/tests/unitutil/cxml.py/Element.nspfxs