// It additionally reports whether caseRange contained a mapping for r.
func to(_case int, r rune, caseRange []CaseRange) (mappedRune rune, foundMapping bool) {
	if _case < 0 || MaxCase <= _case {
		return ReplacementChar, false // as reasonable an error as any
	}
	// binary search over ranges
	lo := 0
	hi := len(caseRange)
	for lo < hi {
		m := int(uint(lo+hi) >> 1)
		cr := caseRange[m]

}

func TestSpecialCaseNoMapping(t *testing.T) {
	// Issue 25636
	// no change for rune 'A', zero delta, under upper/lower/title case change.
	var noChangeForCapitalA = CaseRange{'A', 'A', [MaxCase]rune{0, 0, 0}}
	got := strings.ToLowerSpecial(SpecialCase([]CaseRange{noChangeForCapitalA}), "ABC")
	want := "Abc"
	if got != want {
		t.Errorf("got %q; want %q", got, want)
	}
}

func TestNegativeRune(t *testing.T) {