code: func (c *contextT) Format(f fmt.State, ch rune) {
  	if ch == 'v' && f.Flag('+') {
  		fmt.Fprint(f, c.ctx)
  		return
  	}
  	buf := pool.AllocBuffer()
  	list := List(fromContext(c.ctx))
  	list.writeToBuffer(buf)
  	f.Write(buf.Bytes())
  	pool.ReleaseBuffer(buf)
  }
docs: // Format implements the fmt.Formatter interface. If
  // the context is printed with "%+v", then it prints
  // using the String method of the wrapped context.