docs: def iter_fields(self):
          """
          Iterate all fields as a sequence of (path,name,value) tuples.
  
          :return:
          """
          def generator(path, values):
              for name,value in sorted(values.items()):
                  if isinstance(value, ValueTree):
                      for inner in generator(path + name, value._values):
                          yield inner
                  else:
                      yield (path, name, value)
          return generator(Path([]), self._values)