Why does strict mode activator "use strict" string?

Question

Do not confuse it with the desire to learn how strict work works, but why is strict mode activated with 'use strict';or "use strict";in contrast to a type expression use strict;?

Answer 1

use strict; will cause an error on JS machines that do not support strict mode.

Using a string is backward compatible.

Answer 2

, . , ECMAScript a.k.a javascript . , ? , 'use strict' , use strict. , .