func isIdentRune(ch rune, i int) bool {
	if unicode.IsLetter(ch) {
		return true
	}
	switch ch {
	case '_': // Underscore; traditional.
		return true
	case '\u00B7': // Represents the period in runtime.exit. U+00B7 '·' middle dot
		return true
	case '\u2215': // Represents the slash in runtime/debug.setGCPercent. U+2215 '∕' division slash
		return true
	}
	// Digits are OK only after the first character.