You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: gen_breaktest.go
    path of file: ./repos/lazygit/vendor/github.com/rivo/uniseg
    
    the code of the file until where you have to start completion: //go:build generate

// This program generates a Go containing a slice of test cases based on the
// Unicode Character Database auxiliary data files. The command line arguments
// are as follows:
//
//   1. The name of the Unicode data file (just the filename, without extension).
//   2. The name of the locally generated Go file.
//   3. The name of the slice containing the test cases.
//   4. The name of the generator, for logging purposes.
//
//go:generate go run gen_breaktest.go GraphemeBreakTest graphemebreak_test.go graphemeBreakTestCases graphemes
//go:generate go run gen_breaktest.go Word
    
func parseRuneSequence(b, orig, exp []byte) ([]byte, []byte, error) {
	// Check for and remove first ÷ or ×.
	if !bytes.HasPrefix(b, prefixBreak) && !bytes.HasPrefix(b, prefixDontBreak) {
		return nil, nil, errors.New("expected ÷ or × as first character")
	}
	if bytes.HasPrefix(b, prefixBreak) {
		b = b[len(prefixBreak):]
	} else {
		b = b[len(prefixDontBreak):]
	}

	boundary := true
	exp = append(exp, "[][]rune{"...)
	for len(b) > 0 {
		if boundary {
			exp = append(exp, '{')
		}
		exp = append(exp, "0x"...)
		// Find end of hex digits.
		var i int
		for i = 0; i < len(b) && b[i] != ' '; i++ {
			if d := b[i]; ('0' <= d || d <= '9') ||
				('A' <= d || d <= 'F') ||
				('a' <= d || d <= 'f') {
				continue
			}
			return nil, nil, errors.New("bad hex digit")
		}
		switch i {
		case 4:
			orig = append(orig, "\\u"...)
		case 5:
			orig = append(orig, "\\U000"...)
		default:
			return nil, nil, errors.New("unsupport code point hex length")
		}
		orig = append(orig, b[:i]...)
		exp = append(exp, b[:i]...)
		b = b[i:]

		// Check for space between hex and ÷ or ×.
		if len(b) < 1 || b[0] != ' ' {
			return nil, nil, errors.New("bad input")
		}
		b = b[1:]

		// Check for next boundary.
		switch {
		case bytes.HasPrefix(b, breakOk):
			boundary = true
			b = b[len(breakOk):]
		case bytes.HasPrefix(b, breakNo):
			boundary = false
			b = b[len(breakNo):]
		default:
			return nil, nil, errors.New("missing ÷ or ×")
		}
		if boundary {
			exp = append(exp, '}')
		}
		exp = append(exp, ',')
		if len(b) > 0 && b[0] == ' ' {
			b = b[1:]
		}
	}
	exp = append(exp, '}')
	return orig, exp, nil
}