Unspecified Array.prototype.sort() behaviour

The ECMAScript 6 specification declares the results of the following expressions to be "implementation-defined":


["A","C","B"].sort({});


var a = ["A",,"B","C"];
a.__proto__ = [,"D"];
a.sort();


Object.preventExtensions([,"C","B","A"]).sort();


var a = [,"A"];
Object.defineProperty(a,0,{value:"B",writable:false});
a.sort();


var a = ["A",,];
Object.defineProperty(a,2,{value:"B", writable:true, configurable:false});
a.sort();