(function(){
  "use strict"; // <-- Directive Prologue
})()

(function() {
  // Directive Prologue start
  "foo bar"
  "baz";
  '123';
  '';
  // Directive Prologue end
})();

'blah'; // <-- Directive Prologue (top-level code)
/* rest of the code here */

var x;
"use strict"; // <-- NOT a Directive Prologue

(function() {
  1 + "use magic"; // <-- NOT a Directive Prologue
})();