prev = r
				return unicode.ToTitle(r)
			}
			prev = r
			return r
		},
		s)
}

// TrimLeftFunc treats s as UTF-8-encoded bytes and returns a subslice of s by slicing off
// all leading UTF-8-encoded code points c that satisfy f(c).
func TrimLeftFunc(s []byte, f func(r rune) bool) []byte {
	i := indexFunc(s, f, false)
	if i == -1 {
		return nil
	}
	return s[i:]
}

	for _, tc := range trimFuncTests {
		trimmers := []struct {
			name string
			trim func(s []byte, f func(r rune) bool) []byte
			out  []byte
		}{
			{"TrimFunc", TrimFunc, tc.trimOut},
			{"TrimLeftFunc", TrimLeftFunc, tc.leftOut},
			{"TrimRightFunc", TrimRightFunc, tc.rightOut},
		}
		for _, trimmer := range trimmers {
			actual := trimmer.trim([]byte(tc.in), tc.f.f)
			if actual == nil && trimmer.out != nil {