code: func (api *Client) PostMessageContext(ctx context.Context, channelID string, options ...MsgOption) (string, string, error) {
  	respChannel, respTimestamp, _, err := api.SendMessageContext(
  		ctx,
  		channelID,
  		MsgOptionPost(),
  		MsgOptionCompose(options...),
  	)
  	return respChannel, respTimestamp, err
  }
docs: // PostMessageContext sends a message to a channel with a custom context
  // For more details, see PostMessage documentation.