docs: def send(self, stack: Layers):
          """
          Add a message stack to the send list.
          """
  
          if not isinstance(stack, Stack):
              stack = Stack(stack)
  
          if not self.platform.accept(stack):
              raise UnacceptableStack('The platform does not allow "{}"'
                                      .format(stack.describe()))
  
          self._stacks.append(stack)