docs: def scalar_term(self, st):
          """Return a _ScalarTermS or _ScalarTermU from a string, to perform text and HTML substitutions"""
          if isinstance(st, binary_type):
              return _ScalarTermS(st, self._jinja_sub)
          elif isinstance(st, text_type):
              return _ScalarTermU(st, self._jinja_sub)
          elif st is None:
              return _ScalarTermU(u(''), self._jinja_sub)
          else:
              return st