code: func (cs CallStack) MarshalText() ([]byte, error) {
  	buf := bytes.Buffer{}
  	buf.Write(openBracketBytes)
  	for i, pc := range cs {
  		if i > 0 {
  			buf.Write(spaceBytes)
  		}
  		fmt.Fprint(&buf, pc)
  	}
  	buf.Write(closeBracketBytes)
  	return buf.Bytes(), nil
  }
docs: // MarshalText implements encoding.TextMarshaler. It formats the CallStack the
  // same as fmt.Sprintf("%v", cs).