docs: def parse_yaml(self, y):
          '''Parse a YAML speficication of a message sending object into this
          object.
  
          '''
          self._targets = []
          if 'targets' in y:
              for t in y['targets']:
                  if 'waitTime' in t['condition']:
                      new_target = WaitTime()
                  elif 'preceding' in t['condition']:
                      new_target = Preceding()
                  else:
                      new_target = Condition()
                  new_target.parse_yaml(t)
                  self._targets.append(new_target)
          return self