}
			continue
		}
		invalid = false
		b = append(b, s[i:i+wid]...)
		i += wid
	}
	return b
}

// isSeparator reports whether the rune could mark a word boundary.
// TODO: update when package unicode captures more of the properties.
func isSeparator(r rune) bool {
	// ASCII alphanumerics and underscore are not separators
	if r <= 0x7F {
		switch {
		case '0' <= r && r <= '9':