docs: def writeNSdict(self, nsdict):
          '''Write a namespace dictionary, taking care to not clobber the
          standard (or reserved by us) prefixes.
          '''
          for k,v in nsdict.items():
              if (k,v) in _standard_ns: continue
              rv = _reserved_ns.get(k)
              if rv:
                  if rv != v:
                      raise KeyError("Reserved namespace " + str((k,v)) + " used")
                  continue
              if k:
                  self.dom.setNamespaceAttribute(k, v)
              else:
                  self.dom.setNamespaceAttribute('xmlns', v)