code: func (f *Frame) String() string {
  	var buf bytes.Buffer
  	_ = buf.WriteByte('[')
  
  	sep := ""
  	for i := f.Len() - 1; i >= 0; i-- {
  		_, _ = buf.WriteString(sep)
  		sep = ", "
  		_, _ = buf.WriteString(fmt.Sprintf("%q", f.stack[i].Name()))
  	}
  
  	_ = buf.WriteByte(']')
  
  	return buf.String()
  }
docs: // String returns the quoted names of the noders in the frame sorted in
  // alphabeticall order by name, surrounded by square brackets and
  // separated by comas.
  //
  // Examples:
  //     []
  //     ["a", "b"]