docs: def _parametersToDefaults(self, parameters):
          """
          Extract the defaults from C{parameters}, constructing a dictionary
          mapping parameter names to default values, suitable for passing to
          L{ListChangeParameter}.
  
          @type parameters: C{list} of L{liveform.Parameter} or
          L{liveform.ChoiceParameter}.
  
          @rtype: C{dict}
          """
          defaults = {}
          for p in parameters:
              if isinstance(p, liveform.ChoiceParameter):
                  selected = []
                  for choice in p.choices:
                      if choice.selected:
                          selected.append(choice.value)
                  defaults[p.name] = selected
              else:
                  defaults[p.name] = p.default
          return defaults